A story about the JFK assassination, in which an actor (Tom Hanks, for example) plays both JFK and Oswald. They're played by the same actor because, in this story, Oswald thinks he is JFK, and is so troubled by seeing this alternate version of himself making political decisions that he disagrees with, that he needs to kill the JFK-Oswald out of guilt. Of course JFK is not really Oswald's alternate incarnation, but we see everything from Oswald's point of view, so they have to be the same actor.
Or, was something like this a movie already? Sounds like it should have been, if not.
Have you read 11.22.63 by Stephen King?
Great book.
nope. haven’t.
Hint: It’s about time travel. And … well, the title kind of gives it away.
Worth a look. I really liked it. As an American you might enjoy it more as (apparently) the attention to detail is spot on and King researched this era thoroughly – more so than any other novel.