I recently saw an old doco on something I never even thought was possible or plausible, but there is a lot of info people have put out to create this as a topic.
This was whether Paul McCartney as the world knows him is legit?!
I will not put the many links or videos here, but clues from the beatles album covers to things they said about a so called 'William' who is said to have replaced Paul are there to view and make for a compelling if not just interesting story.
I will leave it to your own searching and please hit the post with comments to discern this theroy.
I will however point out that in the abby road picture they are many so called clues, but one I picked up on is possibly, if you turn the picture upside down, "Paul" has a cigarette in hand which is positioned just as if he were giving the world the finger, perhaps to mock for what he knows?!