This trope is about characters who wouldn't fit together now, for whatever reason, but about whom there is a general consensus in the fandom — even in fics focused on another pairing — that they used to date/have slept together at some point in the past.
This does not apply to Canon exes.
May be secondary to another pairing, not considered a threat but treated rather condescendingly, as in the Merlin examples below. Alternatively, it may be a popular ship which assumes that the Foe Yay they have now is due to a horrible, horrible break-up.
- As one of the best examples of Foe Yay Ship Teasing, Red and Blue Kings Mikoto and Reisi (MikoRei) get this.
- So do their thirds-in-command, Saruhiko and Misaki, who have even more Foe Yay moments in the anime and shippy official art (showing them when they were friends before Saruhiko left the Red Clan and joined the Blue Clan).
- In Fushigi Yuugi slash fic revolving around either Tasuki or Kouji, it's very often assumed they're either former lovers or friends-with-benefits, regardless of whatever the central pairing of the fic turns out to be. (Everyone Is Gay, after all.) Canon more strongly seems to indicate they're Heterosexual Life-Partners.
- Also, Hotohori x Nuriko.
- In Spiral, almost any fic featuring slash and dealing with Kanone and/or Eyes, but not being primarily KanonexEyes, will still mention them at least having been together at some point. Kanone is very, very often the psycho and/or dead ex when the author wants to pair Eyes with another guy.
- This is a common occurrence in the Axis Powers Hetalia fandom, thanks to the characters being nations who presumably have had numerous alliances, treaties, and fluctuating relations with other nations over the course of history. While America/Lithuania isn't a hugely popular ship, even some fans that ship America with someone else think that the two probably had a thing going on during the twenties when Lithuania was living at America's house. Similar cases have also been made for England and France, America and Japan, England and Japan and Russia and China. And of course, even the most ardent Prussia/Hungary shippers have to acknowledge that Hungary used to be married to Austria. Though generally not focused on much by canon or fandom, Austria also used to be married to Spain and, it is suggested, France. Austria has been married to quite a lot of people actually. Apparently he really gets around. And there's Russia/Finland, and Sweden/Norway…
- Sometimes after Sakura Kyoko made her first appearance in Puella Magi Madoka Magica, people suspected her of having had a relationship with Tomoe Mami in the past, since she did acknowledge knowing her. They had at least been friends and partners in magical girl activities, but the situation in Kyoko's house made her adopt a paradigm that goes completely the opposite of Mami's.
- In Fullmetal Alchemist fanfiction featuring a Roy/Hughes pairing, it's nearly always set while they're cadets before Hughes met his wife Gracia.
- GoldenEye: The way James Bond reacts to Alec Trevelyan's betrayal seems more like a lover's reaction than a co-worker's. Cue Foe Yay.
- Ben-Hur: It is widely alleged that Massala's actor was told to portray Massala as trying to rekindle his relationship with Judah, Judah's wasn't, hence the impression of this trope.
- Some shippers choose to think that Luke and Leia got into a relationship that eventually ended in between A New Hope and The Empire Strikes Back, before they knew that they were brother and sister, due to the novelization of the first film strongly implying they were going to get in a relationship at the end.
- Harry Potter:
- Dumbledore/Grindlewald, or at least Dumbledore → Grindelwald has been confirmed by Word of Gay.
- Even before Sirius died, most Remus/Sirius shipping was set back when the Marauders were still at Hogwarts.
- Fanon often makes Charlie and Tonks Amicable Exes, apparently for no other reason than the fact that, if you do the math, they were apparently in the same Hogwarts year.
- Heroes has Claude/Bennet, whose fics tend to be set before Bennet tried to kill Claude.
- Giles/Ethan in Buffy the Vampire Slayer, along with various vampire pairings. Spike/Angel in particular has been pretty much confirmed by Word of God.
- Merlin/Will, Merlin and/or Arthur/Lancelot, and past, unrequited or simply unconsumated Uther/Gaius and/or Uther/Nimue.
- Buddies Helo and Kara of Battlestar Galactica are widely regarded to have slept together prior to the series.
- Over on The Mentalist, most people think that Bosco and Lisbon slept together at least once. Lisbon has moved on. Bosco hasn't.
- There is some debate on whether or not Robin and Marian slept together pre-show, prior to Robin leaving for the Crusades. There's no consensus, but fics that assume or confirm that their relationship was consummated are not considered out of the question (even for those that ship another couple). There is also some evidence in the show itself, particularly the deliberate avoidance of the usual "Maid" when referring to Marian. The creators have stated that they went with "Lady Marian" because they wanted to suggest that Robin and Marian had a history together. Of course, there were also several innuendoes in the show that suggested Marian was still a virgin, so the question still remains.
- There is speculation in the Firefly fandom that Kaylee and Jayne hooked up a couple times in the past, in a friends-with-benefits sort of formula. As the only two long-standing crew members to be otherwise-unpaired, both of whom have lines about having to take care of themselves as a result... it kinda makes sense.
- There've been a lot of serious hints dropped that Harvey and Donna on Suits were once in a romantic relationship. As of episode 3.06, a one-night-stand has been confirmed.
- The idea that KC and Bianca have slept together at least once seems to be one of the few fully agreed upon and common opinions in the DTC ("Degrassi" Tumblr Community).
- There was an absurdly popular Glee fan theory for a while (back when a lot of viewers were holding out for Sam to be Bi the Way) that Sam had transferred from Dalton and he had dated Blaine while there. More recent developments (namely, Sam's poverty and continued lack of interest in guys) have put this to rest.
- Doctor Who: Many Doctor/Master fans assumed that the two went through a break-up of some kind back on Gallifrey, especially given that the Expanded Universe made it explicitly clear that Theta Sigma and Koschei note were friends throughout their time at the Academy, a fact that was hinted in Classic Who and confirmed as part of the canon in The End of Time. The endless Foe Yay — particularly where Ten and Simm!Master are involved — seems to support this. One Expanded Universe writer has said the Doctor/Master relationship only makes sense as "bitter exes".
- Dr. Cox and Carla from Scrubs. It was later confirmed that they went on one date.
- Some parts of Stargate SG-1 fandom have a working theory that Samantha Carter and Cameron Mitchell were an item at some point in the past.
- Tales of Symphonia:
- In slash fandom, if Kratos/Yuan is not happening in the present, it tends to be something acknowledged as having happened in the past.
- In more mainstream shipping, one theory about why Sheena and Zelos have the Slap-Slap-Kiss dynamic that they do is that they dated or at least were mutually interested at some point in the past, but one or the other broke it off/put on the brakes before they could get started, and neither is really over it.
- There's a contingent of Metal Gear fans that think Snake and Otacon had something but broke it off due to Snake's artificially rapid aging and the wish on one or both of their parts to avoid a Mayfly–December Romance. There's a much larger contingent that think of Big Boss and Ocelot as exes.
- Blazblue: A good portion of the fanbase believe that Makoto and Kagura were at least Friends with Benefits once, which makes all their interactions all the funnier. Of course, it's implied a few times that this is indeed the case.
- In Undertale, Toriel and Asgore are a canonical example. They even had two children, one biological and one adopted. The deaths of these two children, and how they reacted, are what led to their breakup, and Toriel refuses even to be Just Friends now. This comes up occasionally in Sans/Toriel fic, and Asgore/Crushing Loneliness is a common joke ship.
- Ace Attorney:
- Mia Fey and Lana Skye. Lana claims that they were "intelectually atracted" in the past, which fandom took as Les Yay.
- Phoenix/Dahlia is unusual example. In the canon they never dated. Major plot twist is that Phoenix was actually dating Dahlia's nice twin sister Iris, and before that he only met Dahlia once when she gave him plot-relevant necklace. Still there are fans who believe that there was a period between getting the necklace and Iris switching places with Dahlia when Phoenix dated actual Dahlia.
- Alexander/Beatrice in The Dreamer. There are several hints within the first pages of Alexander's introduction that can lead to this conclusion, such as Beatrice and Alexander living together for an entire summer and also this little quote: "Ah yes, I remember taking my turn more than once with you that evening".
- Gamzee/Tavros in Homestuck was only canonised long after one half of the pairing went crazy and the other half died, and then left rather ambiguous with no Word of God on the topic at all (it's obvious Gamzee is carrying a torch for Tavros, but whether or not it is requited is not explored). If you believe they ever had a relationship, it automatically becomes dry-docked by the time it is relevant in the story, when Gamzee is rather desperately making out with Tavros's severed head.
- My Little Pony: Friendship Is Magic
- Many fans believe that Princess Celestia and Discord are exes. Though a smaller faction have Princess Luna as the one who was in a relationship with Discord (which would make sense, seeing as Luna had her own dark period).
- Similarly, some fans believe that Rainbow Dash and Gilda had at least a fling when they were younger.
- In Adventure Time, Princess Bubblegum and Marceline are widely believed be a former same-sex couple. And now it's canon!