Skrillex
Imagine finding out that your longtime family friends were actually your birth parents. That's what happened to Sonny "Skrillex" Moore. He was sixteen when he learned the true status of his parentage was that his adopted parents were friends of his biological parents. His adopted parents were Scientologists and he grew up under these teachings, though has since denounced them.
Jack Nicholson
Raised by Ethel May and John Nicholson in New Jersey, Jack always believed that these were his parents. When he was 27 years old, a Time reporter interviewed him and revealed that Ethel May and John were not his parents but actually his maternal grandparents. His real mother was who he thought was his sister, June Nicholson. Sadly, all of these people had already passed away and he never learned their story.