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How was I supposed to know that me and her were both related?
Believe me, if I knew she was my cousin we never woulda dated.—"Weird Al" Yankovic, "A Complicated Song"
The Game The Whole Family Can Play! Haha! Guess what you were doing?
Sometimes in stories, two people meet and just seem destined for romance. Love blossoms in a particular way, or perhaps the two have a loveless Arranged Marriage lying in wait for them instead. But then, someone makes a startling discovery -- genetics has struck! The couple-to-be are related -- and not in the "same species" sense -- and the romance or arranged marriage is called off. The result may be either great rejoicing or great despair. If it's not called off despite the consanguinity issue, intentional Brother-Sister Incest results. Or if the two still want to be together and the author doesn't want to go the incest route, a counter-reveal may show up to prove that the genetics aren't a problem after all.
These days, many people are squicked out by this, so the characters often find out before they tie the knot/do the nasty. This wasn't always the case; Oedipus was very happily (but unknowingly) married to his own mother for many years and had several kids with her before things fell apart (to the extent that The Reveal resulted in Oedipus's mother killing herself and Oedipus himself stabbing his own eyes out), so this is Older Than Feudalism. Still, this trope is surprisingly common in Anime and Manga, as well as other Japanese entertainment, due to much more relaxed views on the subject in Japan.
The surprise relationship is usually either brother/sister, half-siblings, parent/child (much rarer these days than it was in ancient Greece), or, very rarely, uncle/niece or aunt/nephew. Cousins are only borderline squicky since marriage between cousins is actually legal in some regions, and is quite acceptable in many romance novels. In fact, in the Arabian Nights, a man will call a woman he loves or is married to "daughter of my uncle", because in that time marriage between cousins was considered the best option! Because of this, it almost never appears as a plot point since it's a little too close for some folks to be comfortable, but not close enough that the plot demands the relationship break up.
- Onegai Twins played with this one. Each girl came believing that she was the twin sister. They find out about each other, and realize that they each have a 50/50 chance of being the twin. They both fall in love with the main a few episodes after this. The irony being the anime had one of the girls be the guy's sister, and the Novelization had the other one.
- In Neon Genesis Evangelion, Shinji Ikari and Rei Ayanami seem to have some warm fuzzy feelings for each other, but there is a vague connection between Rei and Shinji's mom, Yui. The real kicker is when the viewer learns that Rei was cloned partly from Shinji's mother and partly from Lilith, the mother of the entire human race. This technically makes Rei Shinji's half-sister. Shinji remains unaware of this, he only discovers that Rei is a clone of something. But whether or not their relationship moves past Like Brother and Sister is open to discussion.
- While the manga does seem to lean in a Shinji/Rei direction, it's not that simple. Rei gradually falls in love with Shinji, but doesn't really realize it until it's thrown in her face by Armisael, who does so in a twisted Hannibal Lecture fashion. Shinji isn't romantically attracted to Rei, but feels a connection with her that he can't explain and wants to get as close to her as he can.
- In the Rebuild series, Rei has told her feelings to Asuka who immediately figured out what's going on but took the liberty of not enlightening her. Shinji reveals his own feelings soon after. The real question here is as to how human Lilith actually is, and whether there's enough genetic difference to make it non-incestuous.
- Visually Shinji and Rei both strongly resemble Yui and thereby each other: their faces would look identical if it weren’t for the color difference; Shinji also happens to share Rei’s curvy build. The resemblance functioned as a subtle way to indicate their relation in the original show, and is done so much more blatantly in Rebuild With their only major distinction, their color difference, disappearing at the end of 2.0. They also happen to dissolve inside Shogoki/Yui, metaphorically returning them both to the same womb, and upgrading their relation to twincest.
- Maya's Funeral Procession has Reina Harukawa falling in love with a mysterious girl named Maya Aoki, only to discover that they share a mother (Mrs. Harukawa was the secretary and mistress of Mr. Aoki, he threw her out and took baby Maya away, then she married Mrs. Harukawa and was a part of the plan that killed Aoki and his wife as revenge for him ruining her life and separating her from her eldest child) and thus they're actually half-siblings.
- Koi Kaze has 27-year-old Koshiro and 15-year-old Nanoka having a chance encounter, going to an amusement park together, forming an emotional connection and spark of mutual attraction, and then finding out they're brother and sister in the first episode. This turns into a deconstruction of Brother-Sister Incest, as the two go on to develop a painful and guilt-ridden romantic relationship against their better judgment, fully aware of the devastating implications if their secret got out, but both unwilling to live without the other.
- In .hack//Legend of the Twilight, Shugo and Rena are a pair of brother-and-sister twins who are separated offline in real life due to their parents' divorce ( they each live with their same-sex parent ). They are reunited online in "The World", the MMORPG where the .Hack// franchise takes place, where they become the series' main Official Couple in a Relationship Upgrade. In the original Manga version, they were simply siblings, even showing Rena convincing Shugo to play the game with her, and they never went beyond good siblings. This also probably explains why that anime was quickly declared Canon Dis Continuity by Word of God, with the manga becoming the canon.
- Depending on your interpretation of their relationship before the big reveal, Kira and Cagalli of Gundam Seed. They never really got around to doing anything, but they definitely looked like the usual romantic pairing all the way up to the last five episodes of the series. Word of God is that this was a deliberate reference to Luke and Leia.
- Negi and Asuna, one of the most popular and teased pairings in Mahou Sensei Negima, are very distantly related by the Lifemaker, maybe closer, but how close has yet to be revealed..
- In the Cain Saga, unbeknownst to him the main character's mother is his father's older sister. He then proceeds to fall in love with his first cousin, which was legal in the time period. The problem is, his cousin is his father's older sister's daughter, making her also his half-sister. There are a couple other brother/sister couples as throwaway characters, too.
- Averted in Slayers: Thankfully, Zelgadis stating that Rezo was both his grandfather and great-grandfather turned out to be a translation error.'
- Falan and Ilsaid's dad in Vampire Game did not inform them that they were related, until his son asked for his sister's hand, that is. He then only told his Unfavorite, though.
- Detective Conan has a case with Raita Banba and his fiancee, Hatsune Kamon. Uniquely, it turns out that they're twins and that the latter has Turner syndrome. One of them (Hatsune) suspected something was up after realising that in addition to their identical birth dates, blood types, and unusual ability to know what the other was thinking even when they were silent, that they'd both been adopted after being orphaned in the same fire as infants. When she gets the test results confirming it, she... doesn't take it well.
- Vampire Knight: when Kaname turns Yuuki into a vampire, restoring her memory, she reveals to the audience that Kaname is her brother. Ah, so the Love Triangle will be easily solved, won't it? Wrong. Kaname confirms she's his sister, and states she was born to become his wife. Then he asks the other why they look surprised -- this is very common among pureblood vampires, and in fact their own parents (Juri and Haruka) were siblings.
- The prince and princess from Andromeda Stories, a pair of Half-Identical Twins who were Separated at Birth, get into a relationship before learning of their heritage. Weirdly, they decide to stay together after the truth comes out, citing the fact that incest is fairly common in royal families.
- Kanba and Masako in Mawaru Penguindrum. Doubles as Twincest.
- In a subversion, they do know about their bond and have it clear. It's more of a surprise to the audience than anyone else.
- In Daily Lives of High School Boys, Emi, after days of Cannot Spit It Out, finally finds the chance to confess her love to the visiting Hidenori on a festival, which coincides with his last day in town which happened to be his maternal hometown. But just when she thinks she finally found her chance, Hidenori makes a most surprising revelation to her: they are cousins.
Emi:"And so, I ended my summer break without being able to do a thing."
- A possible example is Millernium "Milly" Feria Noctum and Kane Blueriver in Lost Universe, although, since they are second-cousins, they're probably distant enough to date if they really wanted to, and the very open ending lends serious doubts as to whether Kane survives the end of the series anyway.
- It may never have been revealed to the characters, but Cutter once got it on with Kahvi during a pre-battle orgy, and Kahvi takes up with him while Cutter's family is lost in time, though it doesn't really work out. Much later, readers learned that Kahvi is the daughter of former Wolfriders chief Two-Spear. Cutter is a direct descendant of Two-Spear's half-sister, Huntress Skyfire, making Kahvi his cousin four times removed. Which, especially considering the small gene pool of the Wolfriders, isn't spectacularly close. And with Recognition preventing conception for any but good genetic combinations, the elves may not have an incest taboo.
- Also, if one looks at Scouter/Tyleet's relationship, you'll realize they're 2nd cousins (Brothers Longbranch and One-Eye, Longbranch sires Nightfall, One-Eye sires Scouter, Nightfall has Tyleet, Scouter and Tyleet Recognize). It makes sense, however, that such in-pairings will happen in such a small tribe- so yes, Recognition probably does take care of the biggest problem with incest. Thankfully, however, we haven't been subjected to any -closer- pairings...
- In the Marvel Universe, Kurt Wagner/Nightcrawler finds out that his then-girlfriend is his adoptive sister in magical disguise. This wouldn't have been so squicky except for two things: 1) He kept dating her anyway; and 2) She knew the whole time.
- A story arc in The Fabulous Furry Freak Brothers has Fat Freddy looking for his old home in Cleveland, broke, hungry, and bemoaning his perpetual bad luck. Just then, to his delight, a cute girl appears, befriends him, takes him home, feeds him, and joins him in the bathtub. A car pulls in and she warns "Here come my parents!" - Freddy sees them and exclaims "Holy Toledo, these are my parents too!"
- In Love Kills, a Percy Jackson and The Olympians fanfiction, the main character, Jade, falls in love with Luke only to find out that he's her brother.
- In Naruto Veangance Revelaitons, it turns out that Taliana, one of the girls Ronan regularly has sex with, is actually his mother. Then it turns out that she's a clone of Sakura, making Ronan's relationship with her incestuous as well.
- Star Wars. Yes, Star Wars. Media such as Marvel Star Wars and Splinter of the Minds Eye, produced before Lucas decided Luke and Leia were twins, makes it explicit that they're mutually very interested, but in Splinter neither of them is aware that the other feels the same, and in Marvel Star Wars being interrupted every time their relationship goes beyond declarations of friendship and hand-holding is a Running Gag. Said gag might have been a continuation of a scene cut from The Empire Strikes Back.
- In A Fvnny Thing Happened on the Way to the Forvm, the heroine is a virgin slavegirl arranged to be sold/married off to the Roman general responsible for having destroyed the land where she grew up. She is somewhat reluctant to marry even before she falls in True Love with the hero. But everything ends happily when a set of matching rings proves the general and his perspective bride are long-list siblings, enabling the hero and heroine to marry.
- An extremely squicky reversal in Ator The Fighting Eagle: Ator and his sister Sunya are "in love" and want to marry, only later to find out that Ator was adopted, meaning they aren't siblings at all and can now safely marry. The Squick comes from the fact that they had fully planned to marry even before they learned of Ator's adoption.
- Parodied in Back to The Future (see above quote) where Marty knows that young Lorraine will be his mother, but she doesn't, so she pursues him romantically to his great dismay. She seems to develop some kind of supernatural sixth sense pertaining this as she kisses him, claiming it felt like kissing her own brother.
- Which leads you to wonder how she knew what kissing her brother open-mouth-style felt like..
- This actually isn't all that unrealistic. Kissing is very informative on a subconscious level, as chemicals in the saliva can reveal the level of your arousal to your partner by taste, and it's believed that the Major Histocompatibility Complex has mechanisms in place that cause women to generally be more attracted to men whose MHC genes are more different, thereby encouraging genetic diversity and thus offspring with stronger immune systems. In this sense, it's entirely possible that Lorraine would instinctively recognize that Marty was related to her, or at the very least realize that Marty just wasn't all that attracted to her.
- The movie My Chauffeur flirted with this. As one of several seeming reveals about who the female lead's "real father" was. Apparently Mom got around.
- Oldboy, in which the main character is the victim of an elaborate revenge/imprisonment plot, the final result of which leads him to discover that the woman he has fallen madly in love with is, in fact, his daughter. He, uh, doesn't take it so well.
- This is the whole plot behind Say It Isnt So. Faux-Farrely hijinks ensue.
- The major couple in The Beastmaster turn out to be cousins, though not one person ever remarks on this. Considering that she's described as his half-brother's cousin, maybe they're not blood cousins after all. She could always be the niece of the king's second wife.
- The Japanese film Bubble He No Go has a father sending his daughter (who doesn't know he's her father) back in time some 20 years to find her mother, only to find her younger father instead, who tries to shag her, but she refuses, only to almost give in but then he shortly before realizes that... and so on.
- Parodied in Joe Dirt--in Joe's quest for his lost family, he finds and goes out with an attractive girl who he realizes afterwards was his sister, goes back to tell her and explain why he can't date her (and probably ask her for information), but somehow gets seduced into sleeping with her, then tells her his suspicion. She then explains why she couldn't possibly be his sister, and that they can make love again. Joe puts on a mischievous face and the camera cuts back to the outside of the house... as nothing happens.
Jill: Would it help if you went back to thinking I'm your sister?
Joe: What?! Like I'm some sort of white-trash perv?!
Cut to the outside of the house, the foundations shaking and a nailed-up hubcap clattering off to orgasmic cries:
Jill: I'm your sister! I'M YOUR SISTER!
Joe: AAAAAAAAAHHHH YER MY SISTER!
Joe then assures the radio people he's telling the story to "No, that last part didn't really happen, I just thought it'd be funny."
- Becomes a main plot arc in Incendies when the twins discover when their mother sent them to find a lost brother and their lost father, that the person is in fact the same!!!
- Code 46 deals with a future where, due to extensive cloning, there is a likelihood of a close genetic relationship between perfect strangers. Maria becomes pregnant by William, only to discover that, biologically, she's his mother; due to the laws, the baby is aborted and Maria's memories are modified to forget she ever met William, but unfortunately, nobody told William. He finds her again, only this time their intimacy triggers an implanted suggestion, causing Maria to turn herself and William in, this time resulting in a memory wipe for him and for her exile with her memories intact.
- Played for laughs in Dirty Work: the two best-friend protagonists find out they are actually half-brothers. One of them becomes upset with the revelation and the other cheers him up by reminiscing about their childhood:
Mitch: Hey, hey! Hey, you remember in 5th grade when I was under the monkey bars and I sneaked a peek at your sister's underwear? Remember that? Hey, no no! I was sneaking a peek at my own sister's underwear!
Sam: That's right! Yeah, and then remember in the 12th grade, you had sex with her?
Mitch: [short awkward silence] Okay, enough reminiscing.
- In Lone Star two characters that had dated in high school over their parents' STRONG objections reconnect as adults. They later find a photograph of his dad and her mom and realize why their parents were so opposed to them dating, namely, that they're half-siblings. But they're very much in love and she says that, due to complications in her last pregnancy, she can no longer have children. It's implied that they will stay together.
- In Tromeo and Juliet, the eponymous pair find out at the end they're brother and sister, but decide to get married anyway. In true Troma fashion, they have hideously deformed kids.
- Kind of inverted in Meet the Robinsons. Louis goes to the future, spends time with the Robinson family, and begins to see Franny as a bit of a mother figure (Even actually calling her mom and almost being adopted by her at one point) before finding out that she is actually his future wife. One wonders how he wasn't the least bit squicked out when he meets her for the "first time" in the past.
- In the film Jean De Florette Papet and his nephew Ugolin drive a hunchback to his death in order to get his land. In the sequel Manon of the Spring Ugolin sees the hunchback's daughter Manon bathing in a pond and falls desperately in love with her. He commits suicide when she rejects him. At the end his uncle Papet learns that Manon's father was his long-lost son. That means Ugolin was in love his own niece.
- In the Michael J. Fox film, The Secret Of My Success, Brantley is asked to escort the wife of his boss to her country home. She takes an immediate liking to him and convinces him to stay for a swim, which leads to her seducing him. Not long after, Brantley realizes that she is his Aunt Vera (by marriage, as his boss is his blood-related uncle, Mr. Prescott). Brantley is disgusted, but Vera isn't - she later pursues him sexually.
- In Curse of the Golden Flower, Chan and Wan eventually find out they're half siblings, and take it about as well as you'd expect.
- In Japanese film Inugami, Miki and Akira discover that they are mother and son. They also discover that Akira is a product of another, similarly themed trope.
- Invoked in the Spanish film Km. 0 - a woman hires a gigolo for an extra-marital fling, then comes to believe he's the son she gave up for adoption years earlier. The actual son turns out to be the gigolo's roommate, to her great relief.
- In Zathura, Lisa immediately starts harboring a crush on the astronaut once she awakens after having been being frozen for most of the movie. He tries to brush off her advances, presumably because she's jailbait. Later in the film it's revealed that the Astronaut is actually her little brother Walter from an alternate future. (Since it's a space-themed sci-fi film, this could debatably be considered a loose Star Wars reference.)
- In the film An Awfully Big Adventure, Alan Rickman's character, an aging actor, seduces a teenage girl, only to find out later that she's his daughter. he commits suicide when he finds out
- In Frances Burney's 1778 novel Evelina, the eponymous heroine saves one Mr. MacCartney from suicide, since he believes he fell in love with his sister. MacCartney grows to idolize his savior Evelina in a quasi-romantic fashion. However, at the end of the novel, Evelina is revealed to be his real sister, while his original beloved was an unwitting (and unrelated) impostor.
- Henry Fielding seems to like to subvert this trope for particular effect: In Joseph Andrews, the hero thinks for a while that his childhood sweetheart is his sister; while in Tom Jones, a random one night stand is later seemingly revealed to be the protagonist's mother... Oh NO! Our hero has done something legitimately bad! Fortunately, this is later resolved to be a lie.
- Pyramids by Terry Pratchett features a pair of romantically inclined half-siblings who eventually figure it out (before getting seriously involved). This one might be a Shout-Out to Star Wars, as the non-related male love interest is a Loveable Rogue smuggler with a Cool Ship. (Also there's a bit of a twist, what with them being royalty in Fantasy Counterpart Egypt, where royalty traditionally marry relatives, so the Morpork-educated brother is probably the only person in the kingdom who has a problem with it.)
- In Orson Scott Card's Speaker For The Dead, Miro discovers his mom was cheating on his (sterile) dad with Libo, which makes him and his girlfriend half-siblings. Miro doesn't care, but the girl does. Tragedy ensues.
- In the Peter David novel Sir Apropos of Nothing, the title character eventually falls in love with the princess he's guarding. But the morning after they've consummated their love...he finds a flame birthmark on her hip, which suspiciously looks like the one on his. Further, it's revealed (though to Apropos only) that the princess is the illegitimate daughter of the Queen and the court jester... and that answers Apropos' question of who his father is, as his mother was raped by a gang of knights... and a shadowy figure that matches the description of the court jester.
- JRR Tolkien's The Silmarillion includes the tale of the unfortunate Turin Turambar, whose sister Nienor was born after he left the family, causing them not to meet until she, having gone to look for him, has had her memory erased by a dragon. Therefore not knowing who she is, they get married and she even gets pregnant, but then the dragon restores her memory and she promptly commits suicide. Turin does the same shortly afterwards.
- In One Hundred Years of Solitude, the biggest fear of the matriarch Ursula is that some of their descendants born with a pig's tail, in the fear that it could be the end of both her family and the town. This finally happen long time after her death, when the last members of the family, Amaranta Ursula and Aureliano Buendía, aunt and nephew respectively, mate and give birth a pig-tailed baby who is eaten by ants, after his mother dies in childbirth and his father forgot to take care of him because of his deep grief. Both lovers were unaware of their real relation, and Aureliano Buendía only discovers it in the last page of the novel, just seconds before the destruction of the town.
- In Poppy Z. Brite's novel, Lost Souls, a teenage runaway called Nothing meets up with a trio of real vampires led by the captivating Zillah, and becomes Zillah's lover. Halfway through the novel, it's revealed that Zillah is Nothing's father.
- Though this editor is not sure it's ever explicitly explained, Thieves' World badasses Tempus and Cime seem to be brother and sister and seem to be laboring under various curses related to this (or effects of mitigators). It seems to have driven them both Axe Crazy, though in different ways.
- Stated in Janet Morris' A Man and His God, they are definitely brother and sister.
- In the novel The Shadow of the Wind, Julian, an illegitimate child who doesn't know who his father is, has a secret relationship with Penelope, the daughter of a rich man who mysteriously decided to take Julian in and pay for his education. It is, however, not until years later, long after Penelope has died giving birth to Julian's child, that he learns that she was actually his half-sister.
- Julian never actually finds out, Daniel decides not to tell him in the end for obvious reasons.
- In the novel Moll Flanders by Daniel Defoe, Moll unknowingly marries her half-brother (her mother having abandoned her as an infant) and has two children with him. Upon discovering the truth, the dissolves the marriage and flees Virginia for England, leaving her two children behind.
- In A Song of Ice and Fire, Theon Greyjoy's unrecognized tomboy sister practically seduces him until The Reveal to purposely mess with his head.
- In Robert A. Heinlein's Friday, the eponymous Friday has a bit of a crush on her father-figure employer, who is later revealed to actually be her father... or at least a male who contributed some of her DNA, Friday's genealogy being somewhat non-traditional.
- In Juliet Marillier's novel Son of the Shadows, the protagonists' sister, Niamh, falls for a druid. When her family finds out, they marry her off in a strategic alliance without telling her that the reason they're so horrified is because the druid (Ciaran) is actually the son of her mother's evil stepmother, thus making him her half-uncle. Oops.
- Their relationship is later vindicated though. Their daughter turns out to be the child of the prophecy, ending a longstanding feud with Britain over sacred ground.. Unfortunately, Niamh never lived to see this, having been pushed off a cliff by the aforementioned evil stepmother when the child was a toddler.
- When you look at their family tree, Liadan and Bran/The Chief are second cousins.
- In Lirael by Garth Nix, Price Sameth shows some interest in Lirael, without knowing she's his aunt. At the time she didn't know either, but she's not interested and puts him off. Later, Nick just assumes they're engaged when she sees them together, and when he gets set straight and says she looks too young to be an aunt, Sam messes with his head for fun by telling him that she has a marvelous skincare regimen, and Lirael hastily mutters that she's much older than she looks.
- In Kafka on the Shore by Haruki Murakami, Kafka begins to have a sexual relationship with an older woman who he suspects might be his mother. She denies it, but it is heavily implied both that she actually is his mom and that she already knows this to be true.
- In The Hollow Hills, the second book in Mary Stewart's retelling of the story of King Arthur, Morgause, Arthur's half-sister, bewitches him into sleeping with her, and he only finds out afterward of their relation to one another.
- Subverted in The Elvenbane by Andre Norton and Mercedes Lackey when Valyn is determined to push away Shana even though he admits that she is lovely and knows that she has a massive crush on him. He does this because he suspects that she is his half-sister. He actually goes so far as to set her up with his sidekick in a "handfasting" ritual. However, he picks up the Idiot Ball when he refuses to tell her why he is rejecting her even though she is hurt and angry about it. His excuse? She was Raised by Wolves (or dragons, in her case) and he's not sure if such things matter to her, in spite of the fact that she has already shown herself to be intelligent and fairly well-versed in human and elven culture.
- In the first trilogy of The Chronicles of Thomas Covenant Thomas is the object of open sexual advances by High Lord Elena, who he eventually realises is biologically his daughter, though (thanks to the time discrepancy between the Land and 'our' world) she actually appears to be older than him. Unsettlingly, she knew all along. Though this discovery explains why he finds her emotionally compelling, he continues to wrestle with having some degree of physical attraction to her - made all the more complicated by the fact that he believes his entire experience is a delusion.
- In the Jin Yong novel Demi-Gods and Semi-Devils, all the women Prince Duan Yu has relationship with turned out to be one of his father's natural daughters. Subverted in that Duan Yu was later revealed to be the product of a one-night-stand between his mother and a rival to his father's throne.
- The Kwisatz Haderach breeding program of the Bene Gesserit in the Dune series does rather a lot of this if the crosses mentioned in the books are a representative sample. The people involved are generally unaware, at least at the time.
- The incest is averted in Havemercy, but just barely. Word of God has it that the authors had the brothers in question unrelated in an earlier draft, and deliberately included plenty of sexual tension and the possibility of a relationship between them. Later, they decided to take the relationship in a different direction, and proceeded to erase all hints of UST between them. They were fairly unsuccessful, though, as most of the readers picked up on it anyway. Since the fact that they're brothers is hidden until near the end of the book, almost all of the readers were already shipping them by default by the time they found out. And once the ship has sailed, well, there's no calling it back to shore. It became arguably the most popular pairing of the fandom for a long time, and the Squick was almost completely ignored.
- In The Mists of Avalon, a feminist retelling of Arthurian legend, Viviane sets Morgaine up to sleep with her half-brother Arthur as part of a religious ritual. Neither of them recognized the other until after it was too late, and both were suitably freaked out.
- Happens not once, but twice in The Stone Dance of the Chameleon. Carnelian and Osidian meet in secret and have a passionate affair. Then it turns out that Osidian is the God-Emperor's son, making them cousins, since Carnelian's mother is the emperor's sister. Later, though, it turns out that Carnelian's father is actually the emperor himself - which is not atypical in the ruling house, Osidian's mother being the emperor's other sister. Making them, you know, brothers. In case you hadn't noticed, this is one messed up family.
- In the crime novel Lie To Me by David Martin a man kills himself rather messily after finding out that his young wife is really his long-lost daughter. He is particularly distressed by the revelation that she always knew he was her father, but married him anyway.
- Subverted in the Mortal Instruments series. Clary and Jace are revealed to be siblings at the end of Book 1. They spend all of Book 2 and most of Book 3 angsting about their attraction, until it's revealed that Jace was adopted. Played straight with Sebastian/Jonathan, Clary's actual brother, who kisses her despite knowing full well that she's his sister.
- The Monk: As if raping Antonia wasn't enough, Ambrosio later learns she is his much younger sister.
- In the final Lensman novel, Children of the Lens, it's all but stated that the Kinnison kids (one boy, four girls) will be the progenitors of the Arisians' replacements.
- In Sherlock in Love, Sherlock Holmes finds himself falling in love with the astoundingly intelligent and musically-gifted Violet Sigerson. And then finds out that she is his half-sister, due to his mother's marital unfaithfulness. Holmes eventually tries to pursue a relationship, but Violet will have none of it and fakes her death to stop him forever.
- An unusual example in True Blood, in which vampire Bill finds out his human squeeze Portia is actually his 3rd great-granddaughter.
- Happened in a 2007 plotline in the Soap Opera Holly Oaks.
- Occurred in at least one plotline in Law and Order SVU The girl was the product of her mother's affair with the boy's father, and when the two began dating due to accidental reverse psychology (the mothers hated each other - the father was in fact the husband of both and living a double-life, known about by one of the wives the whole time) the girl is accidentally killed by her father when he reveals to her that he is the boy's father too. The autopsy reveals that the girl was pregnant when she died and that the boy was the father and that he was related to her. The boy is horrified and vomits in Stabler's office. The boy's mother kills his father when she finds out that he was planning on leaving her for the girl's mother, who was jailed for her part in the myriad crimes going around, with whom he also has a son, the boy's half-brother, and leaving the two new half brothers without any parent not in prison.
- One episode of House had a young married couple who both turned out to share the same rare genetic disease... because unknown to the couple, the man's father had slept with the woman's mother and they were half-siblings.
- On top of that, the half-brother wants to stay together; while the half-sister is disgusted. The episode ends without resolving the situation, leaving the brother/husband hoping that she'll come back while Foreman (who supports the relationship) keeps him company.
- Hispanic soap operas used to love this so much, but it has faded in recent years. The ultimate parody of how this used to be done is the song "María Teresa y Danilo", where a girl, daughter of the aforementioned characters, is forced to cancel her wedding after discovering that her fiancé is the son of her father... only for it to be revealed by her mother that, in fact, she is not his biological daughter.
- Subverted in one memorable Argentinian case: the main characters find out they're siblings and go their separate ways. As usual, it turns out to be a lie. Only it's actually true... and their father has decided not to tell them. They marry and live happily ever after.
- "Shame and Scandal" (1965).
- As the World Turns: Holden and Lily are one of the show's biggest supercouples. Lily is also the biological daughter of Holden's sister Iva. Who fortunately turned out to be adopted herself so it was not incest after all.
- Red Dwarf: it was revealed that Lister's ex-girlfriend Kochanski is actually his mother. In the next series, Lister still uses a sexual-magnetism virus to seduce her in an elevator despite his knowledge of this and it nearly works. Then again, Red Dwarf is not known for its continuity, and the revelation of Lister's parentage was probably not carried over from one series to the next. This editor certainly hopes so.
- Then again, Lister also discovered at the same time that he was his own father, which probably trumps any genetic relationship concerns.
- Well, if he is his own Father having had sex with his Mother is rather required...
- It also makes Lister God.
- Cat, and his species, were descended from one pregnant housecat. Just as well that he was the last of his kind and didn't have anyone to mate with...
- They also could also be a race of Half-Siblings if you take into consideration that female cats can actually get pregnant from two (or more) different males in a single litter.
- In the 2007 remake of Flash Gordon Aura and Terek were in place to start up a romantic relationship, only for the eponymous hero to burst into the room to inform them that they are siblings. Later, it turns out they're twins.
- On Just Shoot Me, Jack's handsome new ex-marine new trainer keeps trying to ask Nina out. Nina, who usually Really Gets Around, keeps refusing, much to her surprise. It is at episode's end that she discovers why she's not attracted to him: they're cousins.
- In another episode an old female friend of Jack's shows up with her son, and he and Maya show signs of being interested in each other. Jack, however, is horrified, because he had an affair with this friend right before her wedding and the timing would line up with him being the young man's father. Eventually she reveals that she secretly got a sample of Jack's DNA years ago and tested it, showing he's not the father. By this point, however, Nina's broken the news to the would-be couple, and the man is horrified.
- In the Thirty Rock episode "The Head and the Hair", Liz and the Hair find out right before kissing that their grandparents are cousins. He seems a little more comfortable with it than she is:
The Hair: I think we're third cousins.
Liz: Yeah, I'll see you at the reunion.
- On Grounded for Life, Lily made out with a guy at the funeral. She later learns he was her cousin. Then she is somewhat relived when she learns he was a cousin by marriage but squicked again when learning they're cousins by his marriage.
- On Green Wing, Guy Secretan doesn't find out Joanna is his long-lost and presumed-dead mother until after they've slept together. And it's been caught on tape.
- The Korean soap opera Winter Sonata is Marmalade Boy if Yuu went missing, got amnesia, and really is half-siblings with his love interest. Well, in fact he could be instead the half-sibling of his love rival, but the soap just was happy toying with that until the last chapter.
- There is a memorable scene in this drama where one of the rivals, after being clued of the above situation and arguably tired for the on-off situation who has already left her out of the game, ends yelling to one part of the conflicted couple "It doesn't matter if you are really siblings or not, just go out of the country and marry anyway! Abroad nobody is going to know!".
- In Veronica Mars, Duncan Kane broke up with Veronica because his mother told him she was his half-sister. After the first season finale revealed Veronica and Duncan weren't related, they got back together (until Duncan got Put on a Bus).
- In the Dollhouse episode "Haunted", Echo gets imprinted with the personality of a wealthy woman who wants to attend her own funeral. The woman's son makes a pass at her; she's suitably disgusted.
- NCIS season 6 episode "Heartland" had the team go to the mining town of Stillwater (coincidentally Gibbs' birthplace) where it was revealed the hospitalized Marine and his childhood friend, who remained in Stillwater waiting for him, shared the same father unbeknownst to them both.
- On Nip Tuck, the Carver and the female police officer investigating the case are siblings. Who are sleeping together. In season 5, Christian finds out that he fathered a daughter when he was in college. She just happens to be Matt's new girlfriend. The Squick comes in when once Matt realizes that he's slept with his sister, he wants to marry her and goes to a website to show that any children they might have would be normal!
- All right, we'll be fair: Justin Crowe wasn't actually aware that he'd made creepy passes at two close female relatives. After all, only his sister-lover actually knew that the new maid was Justin's illegitimate daughter. Not that that necessarily would have stopped him. At all.
- On the British soap Emmerdale Maisie Wylde and Ryan Lamb are caught in bed together, and are promptly informed (after many months of hiding this from them) that they are half siblings. Which disgusts both of them and wind up sending Maisie into rehab and getting their father shot.
- On MTV's late-night, sex-advice talk show Loveline, a man called in asking what to do after discovering his pregnant girlfriend is his half-sister (his mother was estranged for years and the girl was racially-mixed, so he had no idea at first).
- On Smallville, when Clark meets Kara (aka Supergirl), they seemed a little attracted to each other. When Kara's comment about her father Zor-El causes Clark to realize that they are cousins, he backs up, clearly disappointed.
- Kamen Rider Double has a strange example that's not quite playing with and may be a Relationship Writing Fumble or may have been intentional. Phillip is really the brother of Wakana but doesn't know it at the time. He's close to her and plans to leave town with her. Then it turns out that she's really his sister. Once the reveal is made there's no change in plans or attitudes at all (although things change for other reasons) and the audience is apparently supposed to accept that "I care for this girl I know" and "I care for my sister" were exactly the same thing all along. There isn't even a Lampshading.
- Any Ryoutarou/Hana fics that were ongoing when it was revealed that she was his niece had to take this route. At least they got off better than the Yuuto/Hana shippers...
- On Dallas, the writers revealed after a few seasons that the Ewings' farmhand Ray was Jock Ewing's illegitimate son, having forgotten that in the beginning of the series, he had been having an affair with Jock's granddaughter Lucy. After realizing what they'd done, they made sure to never reference the affair again, though it was never actually denied to have happened.
- In a Season 5 episode of The A-Team, "Family Reunion," Face helps an attractive woman come to terms with her fugitive father reentering her life. Afterwards, he tells Murdock that he's going to ask her out after their mission is over because he's never met anyone else he's "felt so at ease with." Murdock starts insisting that she's not Face's type because he and the audience both know, due to dramatic irony, that this beautiful woman is actually his half-sister, and her fugitive father is also his.
- In season 3 of Sons of Anarchy it is revealed that Jax Teller and Trinity Ashbey are both John Teller's children. Ony a few people know of this and since Jax lives in California and Trinity in Northern Ireland they do not see the need to tell them. When Jax comes to Ireland he and Trinity quickly hit it off and are about to have sex when their mothers walk in on them.
- This was in an episode of Midsomer Murders a man had 'spread his seed far and wide'--you could hardly turn a corner without finding one of his bastards. One couple didn't meet until they were both in graduate school in Canada and got married, only later realizing they were half-siblings; she was squicked, he didn't mind.
- On Gilmore Girls, after Lorelai's grandmother dies she asks Emily what her maiden name was, and Emily explains that it was already Gilmore because she and Lorelai's grandfather were second cousins. Lorelai and Rory find this information horrifying, while Emily just notes that it used to be a common custom in well-off families.
- Endgame: When the son of the Huxley Hotel's owner goes missing, it turns out that he's gone on a bender because he discovered that the girl he was planning to marry was really his half sister, because his father had had an affair with her mother. but then it also turns out that his mother had been having an affair too, so his father wasn't really his father, and they were unrelated after all.
- Zig-zagged on Arrested Development; Maeby has an on/off relationship with Steve Holt, who is ultimately revealed to be her uncle GOB's illegitimate son (Played Straight). This prompts the couple to break up, but it turns out that Maeby's mother Lindsay was adopted, meaning Maeby isn't related to Steve after all (Subverted), or indeed her other cousin George Michael, who had been attracted to her since the pilot (Inverted). An adult eventually finds out, however, and decides that regardless of who is related to whom the whole thing is just too weird.
- In one episode of The Love Boat, a woman comes on board with her son, to meet the daughter she gave up for adoption. Before they all get together, the son and the daughter meet, and, not knowing who the other is, they fall in love and have sex. The daughter is freaked out when she meets the mother and discovers who the guy she slept with is. Fortunately the son is actually the mother's step-son, so the couple aren't blood siblings and can get married, but the mother has no idea how she'll phrase the wedding invitations.
- In The Nanny, Fran finally meets a guy who seems absolutely perfect for her: Jewish, a doctor, and understands her. At Fran's cousin's wedding, they see each other, and kiss. Cue Fran's mother...
Sylvia: Oh, Fran, I see you've met your cousin.
(Fran and said cousin immediately jump apart, looking thoroughly Squicked)
- Bored to Death, Jonathon and his girlfriend find out they're half-siblings. Left unresolved due to cancellation.
- In one episode of Boy Meets World, Eric hooks up with a girl at a combined school rave/parents' anniversary party who turns out to be his cousin. While they didn't get anywhere, he's still thoroughly squicked at the situation.
- A subtle one occurs in the relaunch of Battlestar Galactica where Ellen Tigh sleeps with Cavil to free Saul. As it turned out, Ellen was one of the Final Five and was essentially Cavil's mother.
- It was a double-whammy, too. Not only was Cavil designed to resemble Ellen's father, she had also viewed him a son. Just another sign of how deep his misanthropism and hatred toward his "parents" really ran.
- The end of the episode with the Pimp Hat in Less Than Perfect had Owen and his Distaff Counterpart date reveal that one of the many things they had in common was that they both had donor dads who were artists. Claude pulls him aside to tell him that it was very likely they were brother and sister. He retorts that "this couldn't wait until tomorrow?", meaning he wasn't completely against the incest.
- This becomes a motive for murder on a case in CSI: Miami. Dad had a Secret Other Family, son from Family A met up with daughter from Family B, fell in love, and had a baby together. Then son found out...
- In the penultimate episode of Community, it's discovered, during the wedding toasts, that Garrett's new bride, Stacy, is his distant cousin. Chang convinces them to stay married.
- The big reveal of Type O Negative's "Stay out of my dreams" is this trope.
With your straight black hair and emerald green eyes
Hippies pointing "that's Pete's sister in disguise"
Maybe you had uttered those words as a jest
I don't mind the allegations of incest
At the time I thought I could love no other
Till I heard you say that I was your brother
In your e-mail said how much we look like twins
How it turned you on just knowing it's a sin
- Mentioned in the "Weird Al" Yankovic song, A Complicated Song - "How was I supposed to know / we were both related? (I tell you if I) / Knew she was my cousin / we never would have dated".
- The song "Son Don't Go Near the Indians"- The whole time the main character of the Western song is told "Son don't go near the Indians, please stay away." Reverse psychology plays its part, and he goes near the Indians--a lot. He falls in love with a girl there about his age. Near the end, they resolve to get married. Only then does his father explain that his actual son got killed by the Indians, so he stole one of their baby boys, the protagonist, and that his girlfriend is his sister. "And that's why I've always said--'Son, don't go near the Indians, please stay away'"
- Subverted in the related song (most likely a parody) "Son Don't Go Near the Eskimo" which leads the listener to suspect a similar conclusion, making the big reveal (the girlfriend is not his sister, but she has "the coldest nose in Alaska") somewhat anticlimactic.
- In the folk song "I'm My Own Grandpa," the narrator marries an older woman with an adult daughter. The narrator's father then marries the daughter, making the son's stepdaughter his stepmother. Because the narrator is married to his stepmother's mother, he has become his own step-grandfather. Not actually incest, either.
- A real life example was just avoided when Mandy Smith's mother broke up with Rolling Stone Bill Wyman's son. Smith and Wyman were married at the time, giving Smith a narrow escape from becoming her own step-granddaughter-in-law.
- Shame and Scandal subverts this: This young man discovers his dad is also the father of every single one of his girlfriends then learns from his mother that his "dad" his not his real father.
- The song "Butterflies" by Sia plays this on the listeners. It sounds like just a regular song about lingering awkwardness in a relationship, until the very last line right at the end of the song, when she casually remarks "Because we came from the same cocoon".
- Cornelis Vreeswijk's "Incest Song" has a similar structure an example named above: Boy meets girls, falls in love. Dad intervenes, claiming they are his sisters. Boy then talks to mom, mom: "Oh, don't worry, he's probably right but he's not YOUR father anyway..."
- Frank Zappa's "Magdalena" is a lengthy and detailed confessional by a Canadian maple syrup salesman to his teen-age daughter of what he'd like to do to her.
- There's also "Brown Shoes Don't Make It", with this exchange, repeated three times:
Man: If she were my daughter I'd...
Girl: What would you do, Daddy?
- The protagonist of the Chinese classic Dream of the Red Chamber is first cousins with both of his main love interests, although this was hardly taboo in China at the time.
- The folk song "Johnny Be Fair" parodies this. The female narrator repeatedly falls in love with men, only for her father to pull out the Parental Marriage Veto because he's their father too. In the end she goes to her mother, who says "he's not really your father, marry anyone you want". It dates back to Elizabethan times and probably further.
- Gothic Americana might not exist as a genre without this trope. Slim Cesna's Auto Club has an EP named "Crossbreeding Begins at Home." Similarly, about half of Jay Munly's oeuvre seems to rely upon this trope. If you're curious, look up the lyrics to "Big Black Bull Comes Like a Caesar" and "There's a Goose Walking Over My Grave." Beware the Squick, though.
- Oedipus' story in Greek Mythology is particularly squicktastic since he unknowingly married his own mother. They only learned the truth years after having four kids together.
- In The Marriage of Figaro, the character interested in marrying Figaro turns out to be his mother and says something like she always loved him just in the wrong way previously.
- The Ring Cycle. In which Siegmund gets away with Sieglinde, who's his twin sister, and they become the parents of Siegfried, the ultimate superhero. Later, Siegfried marries his aunt, Brünnhilde... (Both the twins and Brünnhilde are Wotan's children. Don't even make me start about Wotan's love interests, he's a Casanova.) And in some performances, the Gibichungs are pretty suspicious too.
- As Anna Russell puts it, though, Gutrune Gibich is the only woman Siegfried has ever met, in his entire life, who wasn't his aunt.
- Which makes a great soundbyte, but is sadly untrue, because even if one does not count his mother Sieglinde and the nameless women (servants etc.) in the crowd scenes in Götterdämmerung, Siegfried meets the three Rhinemaidens (daughters of Father Rhine) shortly before his death.
- As Anna Russell puts it, though, Gutrune Gibich is the only woman Siegfried has ever met, in his entire life, who wasn't his aunt.
- This happened all the time in porn in the 70s and 80s. This plot device has since been less frequent. Doesn't mean some people aren't turned on by it.
- Well, actually ... the "oh noes we're related" type of incest plot was fairly rare, while deliberate, conscious incest was not uncommon.
- Although there were a few very rare cases of actual incest, most of the time they just paired two people up who have the same hair color or a similar haircut, and hope the viewers won't look deeper than that.
- Literotica has a section devoted to incest. It gets 90% of site traffic.
- Amber Lynn was a big name in '80s porn. Buck Adams screwed anything that moved. Until the day they were supposed to perform a scene together, and had to admit they were brother/sister.
- Shows up in the plays of Sam Shepard from time to time. Used to deconstruct the American Dream.
- The Roman comedy trope used in A Funny Thing Happened to Me On the Way to the Forum was used more seriously in Gotthold Ephraim Lessing's play Nathan The Wise- the title character is Jewish and it is revealed that his daughter is actually not a blood relative and he is charged with the crime of raising a Christian as a Jew. It ends up turning out that she is the sister of a literal and celibate Knight Templar in play (taking the place of the mercenary of Roman comedy), who other characters had been trying to fix her up with. Both of them turn out to be the children of Saladin's brother and a Christian woman and in at least one translation, the Templar expressed gratitude at the news, as he was not yet prepared for sexual love.
- In The Importance of Being Earnest, it's revealed that Jack and Gwendoline are long lost cousins, but they don't really care and still want to get married anyways.
- The story of Oedipus is the subject of Sophocles' Oedipus the King.
- In Shadow Hearts: Covenant, the hero Yuri meets the babealicious Karin and the two go through many harrowing adventures together. It becomes clear pretty quickly that Karin is falling for Yuri, although he's still pining over his lost love from the first game in the series. However, at the end due to some messing around with the space-time continuum, Karin ends up traveling back in time and marrying Yuri's father...and becoming Yuri's mother. Good thing they never actually got together, eh?
- This makes sense in a twisted way. Considering that Yuri and his father were apparently very similar people, it does make sense that Karin first falls for Yuri in her time and for his father in the past. While they only remained friends, Yuri does manage to convince Karin to wear a very skimpy outfit. The scene become either squicky or more hilarious afterwards depending on how perverted your sense of humor is.
- In the Visual Novel Ever 17, Sara is pretty clearly attracted to the Kid, and vice versa... until it turns out that they're long-lost siblings, at which point they switch gears surprisingly smoothly into a platonic relationship, without so much as a moment of disgust over having flirted.
- In the Baldur's Gate series, Imoen and the main character (if he's male) have the sort of sorta flirty relationship you'd expect from lifelong friends of opposing genders. For that matter, if the main character's female they have the sorta flirty relationship you'd expect from lifelong friends of that sort. When Baldur's Gate II was released and Imoen was not one of the characters with whom you could pursue a romantic relationship, a lot of fans of the original were very surprised and rather disappointed... until you found out that Imoen was your half-sister.
- This is actually brought up in Throne Of Bhaal, the expansion to Baldur's Gate II, if the main character's male. Viconia insists to Imoen that given the number of times he's saved her life, she should serve him in every way. Imoen acts squicked and cites why. Viconia brushes it off, pointing out that the common heritage would hardly one of blood. Imoen then notes that, canonically by that point, the main character has saved Viconia's life at least twice...
- Some people tried to do a mod that allows this relationship; the Imoen Romance mod for Baldur's Gate II is alive and well, and is widely known for near-total freedom of choice in the protagonist's options (ranging from true love to Complete Monster). Imoen is romanceable by both males and females, and to the mod's credit, does not shy away from the incest issue--Imoen in particular has issues with it.
- Fire Emblem: Genealogy of the Holy War has Seliph and Julia; upon meeting they seem instantly attracted to each other, but it turns out that Julia is Seliph's inbreed half-sister, as their mother Deirdre was brainwashed and forced to breed with her half-brother Arvis, who was unaware of their bond. (And Julia's twin brother/Seliph's younger half-brother Julius is the possessed Big Bad). As such, the love points between these two go down as the game advances - unless the player deliberately keeps the two glued to one another or exploits some bugs within the game.
- In the first half, Claud's most popular pairing is with Silvia, who is hinted to be his long-lost sister - but said by Word of God to be a distant cousin.
- Shows up occasionally in fanworks made with The Sims 2: unattended children can be taken away by a social worker, and then adopted into a different family. The adoption code nukes the family connection to the birth parents and creates one with the adoptive parent(s). Some players have used this loophole to have siblings, and twins, adopted into different families, strike up romances. Since there's no genetic penalty for incest, they can even have kids. Read all about it.
- In the PSX RPG Dragon Valor, where one of the two possible final generations of Dragon Valors are always a twincestuous pair of brother-and-sister twins.
- In the Play Station 2 adventure game Drakengard , where it is central to the entire plot, even if the English language version of the game has been Bowdlerized into omitting all but two direct references to incest.
- In the Play Station 2 adventure game Shadow of Destiny, with Eike and Dana living happily ever after, despite secretly being biologically father-and-daughter, in Ending E.
- Well, there's a reason why it's one of the worst endings. And Dana seems to be at least subconsciously aware of the connection on some level and is bothered by it.
- The Casual Game Virtual Villagers allows you to control up to ninety individual village-members with their own names, appearance and skills. The females can get knocked-up. By anybody. That includes their brothers, fathers, and offspring (assuming the offspring is old enough). Thankfully, the game doesn't actually keep track of family relations (which is probably why this is possible), sparing the sensibilities of players who forget or don't pay much attention to the lineage. Or turn their back on randy relations for half a second.
- Used in No More Heroes when Travis is informed that his ex-girlfriend Jeane, who he did sleep with, was his half-sister, which she knew beforehand. He reacts appropriately.
- In Apollo Justice Ace Attorney, we see the protagonist, Apollo Justice. His attractive assistant is Trucy Wright, Phoenix Wright's daughter. They were often paired together in eyes of the fans, until it was revealed that Trucy was adopted, and her last name is really Enigmar. The problem? That was the maiden name of Apollo's mother, and the two were half-siblings. Oddly, it still hasn't stopped the fan pairing from still occurring.
- Happens twice to Dave Strider in Homestuck. He used to hit on Rose (ironically) before learning that they were brother and sister. In Act 6, he and Rose see their mother in a dream, resulting in the following conversation later:
ROSE: You're wondering why I didn't tell you?
ROSE: You're specifically wondering why I wasn't forthcoming with an answer to your question at the time, "hey who was that choice babe in the pajamas?"
DAVE: god fucking dammit
- The original plot of The Nostalgia Chick's "Thanks For The Feedback" would have been a parody of Luke and Leia, with she and The Nostalgia Critic finding out they were related after having sex.
- "Roswell that Ends Well" in Futurama. While stuck in 1947, Fry accidentally gets his grandfather killed and figures that since he still exists, the attractive woman he thought was his grandmother couldn't possibly be. After he does "the nasty in the past-y", Professor Farnsworth explains to Fry that not only is she his grandmother after all, Fry's grandfather is Fry himself.
- Family Guy:
- In "Halloween on Spooner Street", Meg and her friends actually get invited to a costume party, and she goes dressed as a Slutty Cat, complete with mask covering 75% of her face. One game of spin the bottle/seven minutes of heaven later, she's escorted to the closet with someone in an all-concealing Optimus Prime costume. When they're in there too long, the door is opened to reveal it being... Chris. While they're half-naked on the ground making out. They didn't take it well, and lines like "We did so much!" imply there was more than just lips involved, though they seemed to have gotten over it by the end of the episode.
- In "Valentine's Day in Quahog", Stewie travels back to The Sixties and kisses a girl he fell in love with. A second later, she's revealed to be a young Lois.
- A subversion occurs in an episode of King of the Hill, when Bill dates a single mother with two children. Dale immediately becomes suspicious of the girl, Kate, when she starts hanging around Joseph. After secretly running a DNA test on her, Dale finds out that she and Joseph are brother and sister. Dale assumes that HE is actually Kate's father, but everyone else knows that it's really John Redcorn. The rest of the episode has Peggy making sure Joseph and Kate don't, um, explore a deeper relationship.
- A common Plot Twist in soup operas is that some couple found out they are somehow related. Did I say common? SUPER COMMON Plot Twist.
- Days of Our Lives had a scene in which Lucas almost has sex with Cassie. They are only stopped when Rex, Cassie's twin brother, arrives and tells them that they are half-siblings.
- Before that, Cassie had a crush on and kissed her cousin Shawn-Douglas.
- There was an incident, somewhere in this world, where a doctor (secretly) used his own sperm for all his artificial inseminations, meaning that a community now has many couples who might well be half siblings.
- A Minnesota School hosts a pep assembly. Part of it is having various athletes receiving blindfolded special kisses from a secret admirer... Their parents. Hilarity Ensues. But YMMV, very much so.
- In Britain at least, it's not illegal for first cousins to marry, and this troper's grandparents were first cousins. Cousins in the nobility of bygone days often married to keep titles and land within the family. Queen Elizabeth II's husband, Prince Philip, The Duke of Edinburgh, is her second cousin once removed (though some insist he is actually her third cousin - in the British Royal Family and due to Queen Victoria having so many offspring who married into the European royalty/nobility, it gets rather complicated).