One generation back there was a LoveTriangle. Now the [[RomanticRunnerUp losing party]] meets[[labelnote:*]]"Meets" is an important component, since usually it's a sudden development for which the character is not prepared.[[/labelnote]] -- and has to interact with -- the child of the other two. This causes [[{{Conflict}} emotional chaos]]. The character loses the ability to act calmly (or even adequately) whenever a situation arises related to the kid. The effect is greater when the loser is an otherwise calm, MagnificentBastard or [[IdealHero flawless hero]] proven NotSoStoic and NotSoAboveItAll.

If the progeny is of the opposite sex and [[StrongFamilyResemblance resembles the contested person too much]] -- often the case -- it's even worse. Expect a WrongNameOutburst. Not only is it a reminder, one sees the image of the lost love, ''their'' would-be kid, an image of the rival, or a second chance, and so on -- often two or more of these at once. [[AlwaysFemale Usually female]] kid and male ex-rival.

[[AC:Anime & Manga]]
* In ''Manga/HayateTheCombatButler'' Mikoto Tachibana probably had this reaction upon meeting Nagi, who greatly resembles her mother, who Mikoto had an unrequited crush on. Though both Nagi's mother and Nagi herself seem to be not interested in the affection shown because they aren't interested in women, and the arranged marriage was said to be set up by the grandfathers, Mikoto probably had no issue with her son being set up with the daughter.
** Since it's also been implied that Hayate resembles Nagi's mother (and her father), this could also take place if Mikoto were to meet him at some date in the future.
* In ''Anime/ZoidsNewCentury'', Dr. Layon and Dr. Toros loved the same woman, who eventually became Dr. Toros's wife, and mother of his son and daughter. Layon now hates Toros and never meets his son, but actually likes the daughter, who reminds him of the presumably dead Mrs. Toros. ''Not in that way.''
* ''LightNovel/FateZero'' has Kariya Matou, in a sense. He is the UnluckyChildhoodFriend to Aoi Tohsaka that [[DoggedNiceGuy keeps hanging around]] even though she has two daughters with Tokiomi. Even so, he also cares about Rin and Sakura. In fact, when he discovers [[TrainingFromHell what Zouken is doing to Sakura]], he agrees to enter the Holy Grail war on the behalf of the family he'd severed ties with ten years earlier just so he can earn Sakura's freedom. Unfortunately, [[ForegoneConclusion he]] [[VisualNovel/FateStayNight fails]] and ultimately [[spoiler: the war ends badly for him, Tokiomi, ''and'' Aoi]].
** Kirei Kotomine and his relationship with Kiritsugu Emiya and his adopted son [[VisualNovel/FateStayNight Shirou]] are non-romantic ([[FoeYay more or less]]) variant. He certainly isn't unbalanced by the appearance of Shirou, nor does he particularly care about Kiritsugu's biological child [[spoiler:Illyasviel von Einzbern]]. On the contrary, he's quite happy to realize that [[spoiler:unlike Kiritsugu, who was his {{Foil}} in every respect, Shirou is an empty person [[NotSoDifferent like himself]]]].
* Interesting aversion in ''Manga/MedakaBox'': [[spoiler: Fukuro Tsurubami could not keep up with his sister Hato, and had her marry his best friend Kajiki Kurokami in order for this trope to take affect and for him to meet Medaka, the daughter who reminded him of his sister.]]

* ''ComicBook/ElfQuest'' When Rayek meets his former lovemate's children.
* ''ComicBook/UsagiYojimbo'' Once Usagi returns to his hometown, he freezes for a moment when facing the son of his ChildhoodFriendRomance and childhood rival. [[spoiler: As he finds out in a different story arc, Usagi is actually the father and complies when he's asked to [[YouCantGoHomeAgain leave as not to wreck their family]].]]

* This trope is imposed in the ''{{Manga/Berserk}}'' fanfic, [[ "Happy Ending"]]. Griffith, who averts the Eclipse from happening and the Hawks survive, is now in the care of Casca, who is [[spoiler: pregnant with Guts' child; Guts left to pursue his journey after the danger to the Hawks was over, but [[DisappearedDad unbeknowingly left a pregnant Casca behind]]]]. Griffith already knows that he's going to hate the kid, as it's the ultimate proof of [[spoiler: Guts and Casca's relationship and will be the one thing that they will love more than him, which in Griffith's eyes is [[EtTuBrute a mark of betrayal]] ([[{{Yandere}} especially in the case of Guts]]).]] Despite this, [[GiveTheBabyAFather Griffith agrees to be the child's surrogate father when it's born.]]

* ''Songs and Swords'' ForgottenRealms novels: Elaith Craulnober and Arilyn "Moonblade" < Amnestria Moonflower + Bran Skorlskun. "[[WrongNameOutburst Amnestria!]]" was Elaith's first word when he saw Arilyn. Unusual in that later [[spoiler:he mostly got over it, but now ''she'' sometimes overreacts on his past attitude and clashing with her half-elven ideals]].
** Keturah's daughter and [[spoiler:Basel Indoulur]] in ''CounselorsAndKings''. Mostly in a benign "would-be child" way, but this still motivated more activity than is normal for him and even an uncharacteristic murderous rage when he discovered that she's in danger.
* Severus Snape in ''Literature/HarryPotter'' treated Harry the [[SadistTeacher way he did]] because of this. His dad had a mutually antagonistic relationship with Snape. Further, in ''Literature/HarryPotterAndTheDeathlyHallows'' we learn [[spoiler:Snape was Harry's mother's UnluckyChildhoodFriend when they were in school.]]
** Snape was a SadistTeacher anyway (just ask Neville), with a favoritism toward Slytherin students (especially Draco), but there is no doubt that he treated Harry even worse than the norm. According to the internet, he treated Neville the way he did [[spoiler:because if Voldemort had attacked Neville's parents instead, Lily would have lived]], but there's nothing in the series that suggests this is the case. [[KickTheDog It still doesn't justify the way he treated Neville or Harry.]]
* ''Literature/TheCountOfMonteCristo'': Edmond determines to use Mondego's son as a tool of revenge. How this turns out varies among adaptations.
* Briefly, in ''TheGreatGatsby'', where Daisy's child serves as a symbol to Gatsby of the reality of her marriage to Tom.
* ''Literature/WarriorCats'': [[DoggedNiceGuy Ashfur]] was in love with Squirrelflight, who ended up dumping him in favor of Brambleclaw. [[VillainousBreakdown Ashfur had some problems accepting this.]] He even arranged to have Squirrelflight's father killed so she'd feel the same pain he did. The attempt failed though, and Ashfur was never suspected for the attempted murder for a while. He eventually received an apprentice, though, who managed to flare up his issues all over again by being [[spoiler:(supposedly)]] Squirrelflight and Brambleclaw's son, a living reminder of the mate he couldn't have and the future he was denied. They don't get along. While they are never outwardly rude to each other, Ashfur mostly gives Lionpaw the cold shoulder and doesn't try to bond with his apprentice the way all the other mentors do. When Lionpaw demands more intense training, Ashfur takes this request very unsheathing his claws and fighting Lionpaw as if it were a real battle. Ashfur is eager to finish Lionpaw's apprentice training quickly so that they won't have to see each other eye-to-eye anymore.
* From ''ASongOfIceAndFire'': in the first book, preteen Sansa Stark meets Petyr Baelish, the UnluckyChildhoodFriend of Sansa's mother Catelyn...whom Sansa ''greatly'' resembles. He creeps her out in their initial meeting by pointing this out and touching her hair, and things only get squickier from there. The [[ReplacementGoldfish creepiness of the relationship]] isn't helped by the fact that she goes into hiding [[WifeHusbandry posing as his daughter and learning politics at his side.]]
* In the ''Literature/JeevesAndWooster'' stories, Corky, one of Bertie's friends, is a StarvingArtist who needs to stay in his rich uncle's good graces but wants to marry a girl he disapproves of. Jeeves solves this by ghostwriting a book about birds, the uncle's field of expertise, which Bertie publishes under the girl's name. It [[GoneHorriblyRight goes horribly right]], and the ''uncle'' ends up marrying her. Corky is later forced to paint a portrait of their baby, and his resentment of the whole situation seeps through to such an extent that when his uncle sees the finished product he decides to stop supporting Corky on the spot and tells him to get a real job. Jeeves saves the day again by suggesting that the horrifying baby in the picture would make a good comic-strip character and Corky could probably sell it to a newspaper.
* Monica Furlong's ''Wise Child'' invokes and averts a rare gender-flipped example. The town witch Juniper takes a mysterious liking to and volunteers to take in the titular Wise Child after her grandmother dies and she's left with a literal case of ParentalAbandonment. Wise Child later discovers that Juniper and her father had been in love, but her VainSorceress mother "[[MoreThanMindControl persuaded]]" him that he loved her instead. Both mother and daughter think that Juniper took Wise Child in and works her to the bone due to this trope. Juniper later assures Wise Child that she bears her no ill-will (though she is understandably frosty about Maeve), that she loves her like a daughter and that she works her hard only because she believes MiseryBuildsCharacter.

[[AC: Live Action TV]]
* ''Series/AllMyChildren'': Brooke's reaction upon meeting her ex-husband Adam's son with his new wife Dixie. Especially since she and Adam had struggled to conceive and the resulting strain contributed to his affair with Dixie.
** A bit of LaserGuidedKarma years later when Brooke took up with Dixie's ex Tad and got pregnant by him. When Tad was supposedly killed in an explosion, Dixie was forced to accept that ''she'' wouldn't have SomeoneToRememberHimBy--Brooke would.
* A variation on ''Series/{{ER}}''. Elizabeth Corday tries to invoke this when she meets Susan Lewis, an old friend of her husband Mark, when the latter invites her to have coffee, declining with, "I don't drink coffee, I'm breastfeeding." Unfortunately, all it does is make her look incredibly rude, as A)Susan already knew about the kid, so there's no shock factor, and B) Susan had no romantic interest in Mark and was trying to befriend Elizabeth to assure her of this.
* ''Series/GeneralHospital'' Scott's wife Laura ditched him for Luke and they ran off together. Years later when the couple returned to town, Scott's first reaction upon seeing them, as well as their son Lucky, was to punch Luke out, clearly still angry despite all the time that had passed as well as several relationships and marriages for him. Nearly all of Scott's subsequent scenes with Luke and Laura's children have had an undercurrent of sadness and resentment that they aren't ''his'' children with her.
* ''Series/{{Sisters}}''. When the titular characters learn that they have ''another'' sister, the child of their father and his longtime mistress, they gently break the news to their mother, who admits that she already knew and claims to have long since accepted it. Until the woman shows up at Thanksgiving dinner and the mother flips out. She gets over it and later becomes a surrogate mother to her.
* Played with in ''Series/BigLove''. While first wife Barb appears to have no problem with the children husband Bill has with his other wives, second wife Nikki is clearly jealous when she learns that third wife Margene is pregnant again, even though she doesn't even want anymore children. Probably because she fears this will further cement her position as TheUnfavorite.

* A chapter in the tutorial stages of ''[[Videogame/FireEmblemElibe Fire Emblem: Blazing Sword]]'' has Lyn and company seeking the aid of the Marquess of Araphen, a suitor of Lyn's mother before she eloped with a Sacaean nomad, which sparked in him a [[FantasticRacism hatred of Saceans in general]]. At first the Marquess is willing to help, but after he meets Lyn in person, he withdraws his offer, saying that she is "tained by the blood of Sacae". This costs him both his servant Rath (a Sacaean who rides off in disgust; he could stand it aimed at himself, but this goes too far) and a good portion of his fortune (Rath takes it with him as severance pay).
* In ''Videogame/{{Fallout 3}}'', this is implied to be the reason why Dr. Madison Li tends to be so irritable and hostile towards the Lone Wanderer, being the child of the man she fell in love with and another woman. Granted, she's a bit of a MoodSwinger, but it still might explain a few things.
* [[AvertedTrope Averted]] in ''VideoGame/FarCry4''; Pagan adores Ajay for being the son of the woman he loved, rather than hating him for being the son of a man he despised. He even considers Ajay a member of his family, referring to himself as Ajay's "uncle."
* Averted in ''VideoGame/FireEmblemFates''. Fuga was never able to confess his feelings to the woman he loved, and she ended up marrying another man. When she and her husband were killed by Faceless, what did Fuga do? [[spoiler:He took in their orphaned son, Hayato, and raised him as his own.]]

* ''Webcomic/GunnerkriggCourt'' has Sir James Eglamore and Antimony Carver--the daughter of his old flame Surma and the rival and friend Anthony Carver. He falls out of his armor time and again. [[WordOfGod Word of Tom]] [[ says]] that the strong resemblance ''is'' one of the factors--in case the WrongNameOutburst wasn't telltale enough. It seems that he got better with the help (sometimes unfriendly) of Annie and his own colleagues. Renard--who "fell desperately in love with Surma" as well--was shaken too, but in a different way; eventually he settled on being an unofficial ParentalSubstitute.
* ''Webcomic/GirlGenius'' got Baron Klaus Wulfenbach and Agatha Heterodyne < Lucrezia Mongfish + Bill Heterodyne. Circumstances like how Klaus and Lucrezia parted or that he knows [[spoiler:Lucrezia was the BigBad]] -- and just ''how'' dangerous anyone of this family can be -- do not improve the situation.
** And that's [[FromBadToWorse not even getting into how]] [[spoiler: Lucrezia has a copy of her mind hidden away in Agatha's brain [[GrandTheftMe which has taken control on occasion.]]]]
** Zeetha, daughter of Chump, prompts something like this from Klaus as well when he recognizes her fighting style and green hair. The details have not been revealed in-universe, but fans speculate he may have known her mother during his "exile" (and/or ''be'' her father; see the details on his parting with Lucrezia for why he might have been calling himself "Chump" at the time).

[[AC:Western Animation]]
* An inversion from [[BigBad Vlad Masters]], to the eponymous ''WesternAnimation/DannyPhantom.'' Vlad actually ''likes'' Danny (in a twisted, AffablyEvil way). His big dream is basically to steal Maddie back from Jack and make Danny (and Jazz, to a lesser extent) his own adopted children, something which ''they,'' as you can imagine, find rather unsettling.
* An episode of ''WesternAnimation/TheProudFamily'' had this where the failed rival in question was one of the protagonist's teachers (the resulting couple being her grandparents).
* ''WesternAnimation/AvatarTheLastAirbender'' [[PlayedWith Plays With]] this trope: [[NobleBigot Pakku]] becomes quite emotional when he realizes that [[ToBeAMaster Katara]]'s grandmother was his RunawayBride, but ultimately this makes him warm up to Katara and agree to teach her [[MakingASplash Waterbending]]. Also, [[spoiler:he and the grandmother [[DecemberDecemberRomance finally get married]]]]. Also not a normal example, since Pakku presumably never knew the "rival" (Katara and Sokka's grandfather, who was apparently from the Southern Tribe).
* PlayedWith in ''WesternAnimation/TheLegendOfKorra:''
** Lin Beifong does not interact with the children of her ex-boyfriend, Tenzin, until [[Recap/TheLegendOfKorraS1E10TurningTheTides episode 10]], but before that takes out her resentment on Korra, his live-in student, surrogate family member and the {{reincarnation}} of his father Aang (with whom, by Tenzin's account, she got along quite well).
** {{Averted}} when she finally does interact with the Airbabies--Tenzin is nervous about this trope, but Lin seems to have more trouble taking care of them because they're kids than anything. [[spoiler:When Equalists attack Air Temple Island, the kids manage to save Lin from them, despite their young ages. She, in turn, later pulls a HeroicSacrifice so that the whole family can get away]].