Yes, the information you're referring to is correct. Jack Nicholson, the acclaimed actor, learned at the age of 37 that his sister, whom he believed to be his sister throughout his life, was actually his mother. The woman he thought was his mother was, in fact, his grandmother. This revelation came to light during an investigation by a Time magazine journalist in 1974. Nicholson's real mother was a woman named June Frances Nicholson. The details of his family history were kept hidden for many years, and the truth came to public attention during the height of his career in Hollywood.