A character's new Love Interest is eerily similar (in personality, looks, etc.) to an established character—often a best friend of the incompatible sex, or even the character himself. The similarity is sometimes pointed out when someone is listing characteristics of the love interest, and realizes it sounds a lot like a description of someone else they know.
If the character is dating an opposite-gender doppelganger of a friend, it's more often Played for Laughs and mild Ho Yay than to suggest any serious sexual tension between the two friends. It might even be a positive omen for the relationship: the character gets along well with their friend, so the romance may be similarly successful. If the doppelganger and the friend are the same gender, though, it's likely to spark jealousy or suggest that it's the friend they're really interested in.
A common variant is someone dating their own opposite-gender doppelganger, which usually results in the characters becoming repulsed.
This trope does not include instances where the doppelganger is actually a clone or alternate universe double, or other situations where it is the same person or an actual duplicate: this is when someone similar comes along by mundane coincidence.
- In The Beano one of the Crazy For Daisy strips had Daisy dating a guy who looked almost identical to Ernest apart from different coloured clothing (right down to an extra toe and a mole on his bum). In the end he dumps Daisy for a similarly identical version of her to both Ernest and Daisy's confusion.
- In "The Cartoon", George dates a woman who looks a lot like Jerry. When she ends up cutting her hair short (almost identical to Jerry) it weirds George out to the point that he leaves the woman, and decides to take a break from Jerry for a few days.
- In "The Invitations", Jerry gets engaged to a woman played by Janeane Garofalo, who behaves almost identically to Jerry himself. Jerry comes to hate her, realizing that he "hates himself". Of course, she reaches the exact same conclusion, at the exact same time, leading to the only recorded instance of a genuinely mutual break up (not that anybody ever believes Jerry about that part).
- House: Wilson started dating Amber who, being mean and clever, was officially nicknamed "Cut-throat Bitch". House pointed out in conversation that she was basically his female counterpart, his eyes having gone appropriately wide from horror seconds before:
House: Oh my God. You're sleeping with me.
- The Drew Carey Show: at a party, Oswald and Lewis become very attracted to the female counterpart of the other (and vice-versa): Oswald for "Louise" and Lewis for "Olivia." Both sets get creeped out and decide to forget the whole thing once they realize what's going on.
- In a different episode, Lewis and Oswald meet the adult son of a mutual ex-girlfriend who is unsure which of them is his biological father despite his strong resemblance to Lewis due to his equally Strong Family Resemblance to his (unseen) mother. Drew and Kate (but not Lewis and Oswald) deduce that Lewis and Oswald both dated a female doppelganger of Lewis and are creeped out.
- Friends, "The One With Russ": After breaking up with Ross, Rachel goes out with Russ, who looks, acts, and talks just like Ross. Amazingly, the only other character not to notice the similarity is Ross.
- In one episode, Phoebe and her identical twin Ursula date the same guy, who is very confused.
- Similarly, on an episode of Frasier, Daphne goes out with essentially a clone of Niles. Like Rachel, Daphne doesn't notice; unlike Ross, Niles does and is very pissed.
- A much squickier example occurs in another episode, where it turns out that Frasier is in fact dating a doppelganger for his own (deceased) mother — played by the same actress, no less.
- The Sopranos has an example. In the third season Tony starts seeing a new mistress, the beautiful but depressive and temperamental Gloria Trillo. After complaining about her to Dr. Melfi in therapy, Melfi points out that his description of her (much more psychologically than physically) sounds eerily like his recently deceased mother, Livia.
- Actually, almost all of Tony's goomahs are impossible-to-please dark-haired beauties with serious psychological issues. However the most damaged—and the most like Livia—was definitely Gloria (which Tony realized when she snapped at him "Oh, poor you!"—just like his mother!).
- On Mr & Mrs Murder, Peter's ex is noted several times as looking remarkably similar to Nicola. Nicola however insists that she doesn't look 'exactly' like her.
- The Nanny did it twice, once with Max dating an almost identical clone of Fran and once with her dating a guy you could tell apart from Max only by his job. The girls got along pretty well, while the men started hating each other's guts almost immediately.
- On Two and a Half Men, Charlie dated a woman who strongly resembled their mother in terms of attitude, behaviour, etc. Everyone except Charlie could see it, until they met her two young sons, who were remarkably similar to Charlie and Alan, including in terms of how she treated them.
- Molly's fiance Tom in Sherlock is introduced wearing the same outfit and sporting the same sharp features as the titular anti-hero. This is Playedfor Laughs initially but very quickly becomes sour as Sherlock's return appears to cause Molly to become disinterested in Tom.
- In Scrubs Danni is introduced as a female version of JD (right down the the Imagine Spots and Inner Monologues). Later in the series when he's dating her again it's revealed she's much more of The Lad-ette, which is explained as her no longer trying to impress him.
- In Doctor Who, Jo's love interest Cliff Jones is flat-out stated to be pretty much a younger version of the Doctor before he even appears onscreen, at which point the similarities begin slapping the viewer in the face. He and Jo are apparently very happy together, as they are still married as of The Sarah Jane Adventures episode "Death of the Doctor" and have a truly ridiculous number of children and grandchildren together.
- Good Luck Charlie: When Spencer goes off to college, he dates a girl who looks exactly like Teddy, while Teddy dates a guy that looks very similar to Spencer, though not identical.
- In Ned's Declassified School Survival Guide Ned has a crush on and eventually dates Suzie, who has a very similar personality to Ned's Childhood Friend, Moze.
- On Broad City, Ilana dates her same-gender doppelganger in one episode.
- In Lovesick, the season finale has a flashback to when Dylan dates Phoebe, who is the female version of his best friend Luke. When Evie points that out, Dylan decides he has to break up with her. However she breaks up with him, as she has feelings for Luke. They never act on it, and in the present Dylan and Luke find out she passed away.
- In The Big Bang Theory, the guys sign Sheldon up for a dating site as a joke and somehow end up matching him with his female counterpart, Amy. It takes a while for their relationship to turn romantic, and as it's done so, Character Development has diverged them so it's less "Amy is fem!Sheldon" now, but more character changes seem to be bringing Sheldon closer to Amy's new personality. Do not ask fans if this is a good thing.
- Perfect Strangers. After breaking up, Balki and Mary Ann date carbon copies of each other. True to form, neither of them realizes it about their own partners—though Balki does after slipping up and calling the other woman "Mary Ann", but they instantly see it about each other's.
- Exaggerated to the point of absurdity in Man Seeking Woman. After getting turned down by Rosa, Josh begins dating "Bosa," claiming that he has no idea what anyone means when they say Bosa resembles someone he knows. She is, in fact, a flawed clone of Rosa.
- In Avenue Q, Rod ends up dating a guy named Ricky, who happens to be almost identical to his friend, Nicky. However, in a variation, Rod had already been established as being in love with Ricky, but unable to be with him due to Nicky being straight. Nicky himself sets them up, noting that he knows Rod's type, but it's deliberately left ambiguous whether he knew Rod liked him or whether he just guessed well.
- In Angel Moxie, Alex is telling her best (female) friend Riley about her new boyfriend Kevin, who's really into science and math:
Alex: I just realized I'm gonna be dating the male version of you.
Riley: That's a good thing, right?
- In Shortpacked!, Robin sleeps with Jake Manley, who is pretty much an opposite sex clone, during a Cadbury Egg Cereal binge. After she snaps out of it, she realizes he is completely annoying and promptly breaks things off.
- In Dumbing of Age, Danny begins to crush on Amber shortly after breaking up with Dorothy. When the pair run into Dorothy as well as Danny's friend Joe he's immediately Squicked by how similar the two girls look. (Admittedly not identical, but with the same basic body and hair design.)
- A non-canon Shortpacked! strip suggested that after Robin and Leslie split up, Leslie started dating a hyperactive Englishwoman who had become an MP in curious circumstances and been part of a team that defeated an invasion by Venusians (paralleling Robin's personality, position in Congress and role with SEMME).
- In Khaos Komix, Amber briefly dates Mark and it's made clear by her mental comparisons of him to her friend Nay that she agreed to date him mainly because he looked somewhat like a male version of the girl she secretly had a crush on.
- In one storyline of Bobwhite, Ivy breaks it off with a guy (one day after meeting him) because he's essentially a male version of her friend Marlene.
- The Secret Bakery in Questionable Content is a Similar Squad to Coffee of Doom. When Faye learns that Angus used to go there to be insulted by Not!Faye, she teases him mercilessly. Surprisingly, when Marten briefly dates Padma (Not!Dora, who he used to be in a relationship with) nobody comments.