History Main / AFamilyAffair

** After her [[BrotherSisterIncest brother/lover]] Jaime (with whom she was sleeping throughout her marriage to King Robert) is captured by the Starks, Cersei consoles herself by sleeping with their cousin Lancel, who is apparently closely enough related that he resembles Jaime.

** One of the origins of Zagreus and Melinoe is that Zeus slept with his brother Hades's wife Persephone [[BedTrick by disguising himself as Hades]]. [[IncestIsRelative Persephone also]] [[ParentalIncest happened to be Zeus's daughter]] [[BrotherSisterIncest by his sister Demeter]].

While it can involve SettleForSibling and LoveFatherLoveSon, those tropes are usually for when the partner is dead or they're not in a relationship, if they ended up pursuing it at all. Of course, it's possible that it leads to a RemarriedToTheMistress scenario. The cheating partner might find their in-law to be a ReplacementGoldfish to whatever spark they had with their spouse. If the relative turns out to be the father of the spouse's child, it's a FamilyRelationshipSwitcheroo. Usually doesn't have anything to do with IncestIsRelative although some cultures may consider it semi-incestuous unless the partners were already related.

* In ''Film/BumbleBee'', Roy, the corrupt hick who explodes into goop by Decepticons Shatter & Dropkick when they first arrive, apparently attempted (and failed) to cheat on his wife with her sister, and cares more about his car than he does the lives of anyone around him.

* Series/UmAnjoCaiuDoCeu: One major factor in the Medeiros family becoming a BigScrewedUpFamily is protagonist João separating from his wife Naná after she discovered him cheating on her with his sister-in-law Laila in a tryst that resulted in him impregnating her with a HeroicBastard daughter Cuca.

Adultery is considered to be a betrayal on the cheater's behalf, and a major source of drama because of it. And as family is supposed to look out for one another, when the person they cheat with is a relative of the cheated partner it's [[TreacheryIsASpecialKindOfEvil all the more of a betrayal, and thus all the more dramatic]]. Usually it's the wife sleeping with her brother-in-law, or brother sleeping with his sister in-law, though sometimes it's the parent or child. Doing so means they're almost universally considered a {{Jerkass}} for betraying their own loved one's trust, and the affair is usually on the bad end of GoodAdulteryBadAdultery. Of course, it's possible for it to be sympathetic if the relative is far nicer than the spouse being cheated on, or the cheaters wanted to be partners in the first place but had to settle for the other relative. Maybe it's just a sign of a DysfunctionalFamily.

While it can involve SettleForSibling and LoveFatherLoveSon, those tropes are usually for when the partner is dead or they're not in a relationship, if they ended up pursuing it at all. Of course, it's possible that it leads to a RemarriedToTheMistress scenario. The cheating partner might find their in-law to be a ReplacementGoldfish to whatever spark they had with their spouse. If the relative turns out to be the father of the spouse's child, it's a FamilyRelationshipSwitcheroo. Usually doesn't have anything to do with IncestIsRelative although some cultures may consider it semi-incestuous, unless the partners were already related.

* ''Film/KenPark'': The teenager Shawn is sleeping with his girlfriend's mother behind her back and fantasizes about having a threeway with the two of them. Out of the four main characters, whose lives are rife with abuse and dysfunction, his situation is probably the ''least'' psychologically messed up.

* ''Literature/CloudAtlas'': The main reason why Timothy Cavendish is locked up in a home is because he slept with his brother Denholme's wife Georgette. They seemed to have a bad relationship before this, but it certainly didn't help.

** The heroine Jude Duarte starts a relationship with Locke. She later discovers that he is in a secret relationship with her sister Taryn, whom he even later marries. Locke started his relationship with Jude, because he loves to create drama and scandal.
** Locke's mother, Liriope, was a consort of High King Eldred, but she also slept with his son Prince Dain. This ends up costing her her life, since [[spoiler:Dain murdered her after he found out she was pregnant.]]

* ''Theatre/{{Chicago}}'': Velma, like all the other "Merry Murderesses" of the Cook County Jail,is a murderer; she killed her own husband and twin sister. In "Cell Block Tango", her motives were explained to have been blind fury at finding her husband and sister having sex after she left for just a few minutes.

* PlayedForLaughs in an early strip of ''Webcomic/GrrlPower'', as Tony and Olivia are [[http://grrlpowercomic.com/archives/159 half-siblings/cousins]], as the end result of their father achieving a TwinThreesomeFantasy. Grandma keeps a LaughTrack handy for the inevitable infighting between the twin sisters.

** The justification for the Blackfyre Rebellion's cause is the rumors that the current king, Daeron Targaryen, [[MamasBabyPapasMaybe wasn't actually King Aegon IV's son]]. Rather, he was the result of Queen Naerys cheating on his, or rather [[RoyalInbreeding their]] brother and kingsguard Aemon the Dragonknight. Since Dameon Blackfyre was a legitimized bastard of Aemon and Daena the Defiant, he and his descendants would have more of a claim to the throne if it were true. In-universe most believe this is unlikely due to how pious and honorable Naerys and Aemon were, even if they did love each other, and that Aegon himself started the rumor in order to disinherit his son.

** Batman (Bruce Wayne) and the first Batwoman (Kathy Kane) originally had no connection to each other, but after a {{Retcon}} or two, she became the widow of his mother's brother Nathan Kane and therefore his aunt. They fell in love regardless.

* ''Franchise/{{Batman}}'': Commissioner Gordon was originally meant to be [[ComicBook/{{Batgirl}} Barbara Gordon's]] uncle before being retconned to have always been her father. Barbara once discovered that he may have been sleeping with his brother's wife around the time she was conceived, [[LukeIMightBeYourFather implying she may have been his biological daughter]].

* ''ComicBook/WonderWoman1987'': While Aphrodite's parentage is left vague her she cheats on her husband Hephaestus with his brother Ares, and has several children with Ares.

[[YourCheatingHeart Adultery]] is considered to be a betrayal on the cheater's behalf, and a major source of drama because of it. And as family is supposed to look out for one another, when the person they cheat with is a relative of the cheated partner it's [[TreacheryIsASpecialKindOfEvil all the more of a betrayal, and thus all the more dramatic]]. Usually it's the wife sleeping with her brother-in-law, or brother sleeping with his sister in-law, though sometimes it's the parent or child. Doing so means they're almost universally considered a {{Jerkass}} for betraying their own loved one's trust, and the affair is usually on the bad end of GoodAdulteryBadAdultery. Of course, it's possible for it to be sympathetic if the relative is far nicer than the spouse being cheated on, or the cheaters wanted to be partners in the first place but had to settle for the other relative. Maybe it's just a sign of a DysfunctionalFamily.

* ''Film/KenPark'': The teenager Shawn is sleeping with his girlfriend's mother behind her back and fantasizes about having a threeway with the two of them. Sadly, his situation is probably the ''least'' psychologically messed up of all the four main characters, whose lives are rife with abuse and dysfunction.

* In ''Literature/TheFolkOfTheAir'', the heroine Jude Duarte starts a relationship with Locke. She later discovers that he is in a secret relationship with her sister Taryn, whom he even later marries.

* In ''Film/HowToMakeAnAmericanQuilt'', it's eventually revealed that the long-standing issue between sisters Hyacinth and Gladiola is that while Hy's husband was dying in the hospital, Hy slept with Gladdy's husband Arthur.
* In ''Film/BumbleBee'', Roy, the corrupt hick who explodes into goop by Decepticons Shatter & Dropkick when they first arrive, apparently attempted (and failed) to cheat on his wife with her sister, and cares more about his car than he does the lives of anyone around him.

[[folder:Films]]