Weirdly, the actor Patrick Stewart had the opposite thing happen to him, he's discussed it in an interview...

His mother told him as a child that he was circumcised, and he spent his whole life, until he was in his sixties I think, believing that. He only found out differently when he mentioned it in passing to his wife, and she said, 'But you're not circumcised.' He was like, 'What are you talking about? Of course I am!' and she insisted he wasn't. As it happened, the following day he happened to be at the doctor's and asked the doctor to clarify!

God knows how that confusion came about. How could the mother have thought he was circumcised when he wasn't?