Fascinated by stories of the - I guess you'd call it the "stolen identity" genre, like, of the Anastasia Romanov variety. But - from both sides.
Your husband has been at war for thirty years. You married when you were teenagers. The man who returns bearing his name looks... plausible, you don't remember his eyes being quite so blue, but it's been thirty years and it's not like you could ever afford to have a portrait painted. He knows your name and the names of your children and your parents, but there are curious gaps in what he remembers. But war does things to the mind. And if he's kinder than you remember? Kind enough that, maybe, you let yourself believe...
No one has ever looked twice at you, since you're just the maid, until the day a revolutionary bomb goes off, blowing a crater in the summer palace. The famously reclusive duchess and the rest of her household lie dead in the rubble. You know that you and she were the same dress size. You know where her jewels are kept. Most importantly, you know the location of the secret tunnel that leads down to the docks, and to a life overseas that would be torturously hard going for a poor maid, especially one suspected as a thief, but a lot more comfortable for a royal in exile...
The old king's most faithful retainer swears this is the heir to the throne, raised in secret and trained to one day step into his father's shoes. As the usurper as dragged off the throne, she screams that the old king's children are all dead, she made sure of it; no one pays her any heed. (Maybe they should have...)
The man in the tavern is buying drinks for the whole bar before he sets sail tomorrow for the far side of the world. He's got it all figured out - a ship of his own, retirement to a tropical paradise when he gets sick of the pirating life. His lip curls as he talks about the stultifying boredom of the aristocratic world he's already left behind. You find out that his parents recently died, and the estate is in the care of his younger sister, who was only six when her brother first left home two decades since. Between the lines, they sound like a good family; they sound like they love him, the way your family never did. Your heart aches. He shows you portraits, letters, before shoving them carelessly back in his coat pocket. They would be so easy to lift...
It's a surprisingly common concept and I just love it. It's The Return of Martin Guerre; it's multiple 90s romcoms; Agatha Christie pulls it half a dozen times. Sooner or later, it crops up in fanfic for just about any fandom with a royal or aristocratic main character.
And I can see why, because there's so much richness to it. From the outside, it can be anything from a horror story to an unlikely love story; from the perspective of the person pulling off the con, a heist movie or a tragedy or a heartwarming tale of found family. And then there are the longer-term implications: What happens if you wear a mask so long that it becomes who you are? What happens if you come to love the "replacement" to the point where you don't want to find out the truth? What is it like to uncover such a deception a century down the line, to find out that your great-grandfather... wasn't?
Just. Identity stories, man. <3