A distant relative comes to visit and is welcomed warmly by their hosts. There's no doubt in their minds that this visitor is part of the family, even if it's been a while since they last saw each other. The relative makes their contribution to the plot, usually with little to no involvement from the heads of the household.
Once things wrap up, the relative heads back to where they came from. The hosts reminisce about their visitor. One of them mentions how nice it is to have company from their in-laws.
"Wait a minute," says their spouse, "I thought they were from your side of the family!"
This genealogical confusion goes unsolved for the rest of the story. At best, the audience is still left wondering how the relative ever ingratiated themselves into the family in the first place.
There's no impersonation going on, at least not that the audience knows going in. The relative is always welcomed without having to convince their hosts that they're related. Often the relative is a mentor figure or has a mystic quality about them, which is only reinforced by their uncertain place in the family tree.
Also see Ambiguously Related when characters seem like they should have family ties but no one directly touches on it. Compare Mama's Baby, Papa's Maybe for another instance of unclear family relations. Also see Abilene Paradox for a similar dynamic ("Wait, I thought that was you wanted to do...") applied to decision-making rather than family ties.
Examples:
- American Born Chinese: Danny's family gets annual visits from Cousin Chin-Kee, who is a cartoonishly exaggerated Chinese stereotype. After the tension between the boys is resolved and they go their separate ways, Danny tells his parents that Chin-Kee left to go back home early. Dad tells Mom to let her sister know, but Mom replies she thought Chin-Kee was Dad's nephew. This scene caps off a number of reveals, including Chin-Kee being a disguise used by the Monkey King.
- Dude, Where's My Car?: At the beginning of the movie, the two main characters discuss one of their party's guests, and are surprised to discover neither knows him, each thinking he was the other's friend.
- National Lampoon's European Vacation: The Griswolds pass through Germany to visit some distant relatives, who are kind hosts, albeit continually confused by the Language Barrier. After they leave, the German couple admits to each other that they have no damn clue who they were; the Griswolds had come to the wrong house.
- Played for Horror in Weapons (2025). Gladys invites herself into the home of Alex by telling his parents that she's a distant "aunt". However, she's actually a witch who forces Alex to bring her the name tags of all his classmates, using his poor parents as hostages to make him compliant. Most likely, she has no ties to the family at all.
- A joke (which can be found in Good Clean Jokes) relies on this trope. A young married couple had their wedded lives disrupted by the arrival of crotchety, complaining Aunt Emma. Eventually she died, and after the funeral, the husband tells his wife that he doesn't think he'd have been able to bear her Aunt Emma's presence all those years if he didn't love her so much. The wife, aghast, exclaims that she thought the woman was his aunt.
- A similar joke exists where a young woman goes to visit a much older and richer relative. As she enters the mansion, she is followed by a very scruffy dog, who proceeds to wreak havoc inside, making the conversation extremely strained. As the young woman leaves, she is asked to visit again, but maybe leave her dog at home next time. She responds with shock; she thought it was so badly housebroken because it was the older lady's dog.
- The Dark Half: Discussed in the Stephen King novel. Main character and novelist Thad talks about what it was like in his household when he was writing under his infamous Pen Name/alter ego. He compares it to having a bad long-term guest who you dislike but are also a little bit scared of and feel like you have to put up with because he's a distant relative of your wife. He ends the extended metaphor with the following:
Thad: And then one day, after this bad guest has done something like slam the salt cellar against the wall because it's clogged, you say to your wife 'How long is your idiot second cousin going to hang around, anyway?' And she looks at you and says 'My second cousin? I thought he was your second cousin!'
- Diary of a Wimpy Kid: In Hard Luck, Greg mentions the relatives who showed up to the last Heffley family reunion, including Uncle Larry. He doesn't think Uncle Larry is actually related to anyone in the family, but just showed up at one family reunion and came to every single one after that.
- Bewitched: In the episode "The Leprechaun", the Stephenses get a visit from a leprechaun named Brian O'Ryan. Darrin thinks that Brian is a relative of Samantha's since she is a witch, but Samantha and Brian himself both think that Brian is a relative of Darrin's, even though Darrin doesn't know Brian.
- In Community, Garrett and Stacy both assume that an old lady at their wedding is the other's relative. It turns out she's both. This doesn't stop them.
- Murder, She Wrote: In the episode "Something Borrowed, Someone Blue", none of the Mayberrys are quite sure how Cousin Clara is related to them. It turns out she isn't; she just gatecrashes weddings for fun and food.
- The Addams Family (2010): There is a joke concerning Grandma's ties to the family, possibly as a nod to how different incarnations of the franchise have varied on whether Grandmama is Gomez's mother or Morticia's.
Morticia: When your mother moved in, it was supposed to be for two weeks. The weeks turn into months. It's been 12 years now and she's still up there! Unwanted, mocked, tolerated! Smoking weed in the attic. Well, I'm not going to end up like your mother!Gomez: My mother? I thought she was your mother! (Beat) No, seriously.
- Jackie Chan Adventures: In the episode "Demon World, Part 1", Jade's dad tells her that Uncle (i.e., the old man who everyone calls Uncle) is actually his cousin, then immediately asks Uncle with uncertainty, "aren't you?"