When she is your mother. Just ask Jack Nicholson. While preparing a story on the star of Chinatown, which was just being released, a Time reporter called him in June of 1974 to confirm some family facts. Was it true that his sister June, was in fact his mother? And that his father lived in New Jersey?
Nicholson was stunned. The 37-year old actor had grown up thinking that June, 17 years his senior, was his sister. She was actually his mother, and Jack was the illegitimate child she had as a teenager. His grandparents raised him as their own, and neither his birth mother, nor his grandparents/parents, gave away her secret, even on their deathbeds. The truth was verified the same year, by his aunt Lorraine, June's sister.
He's not the only star to discover a re-arrangement of the family tree. Singer Bobby Darin, who at 32-years of age in 1968 was considering a career in politics, got a similar shock when his sister confessed that she was in fact, his mother. Knowing that politics called for complete disclosure, he went back to his musical career, which ended all too soon in 1973, when Darrin failed to take antibiotics before a dental treatment, and he succumbed to heart failure.