Actor Jack Nicholson found out his sister was actually his mother when he was 37.
In April 1937, Jack was born in Neptune City, New Jersey. For 37 years, he assumed that his biological mother, June Nilson, was his sister.
Time magazine researchers discovered, and told him, that his sister, June, was actually his mother. The individuals Jack believed to be his real parents were named John and Ethel May Nicholson.