Troubled actress Mackenzie Phillips reveals a long-held family secret in her new memoir and on the episode of "The Oprah Winfrey Show" airing on Wednesday (September 23): Her late father, musician John Phillips of the Mamas and the Papas, carried on an incestuous relationship with her for years.

Phillips, 49, a former child star of the 1970s and '80s sitcom "One Day at a Time," has battled drugs for years, and she reportedly revealed to Oprah that it was her father who first shot her up with cocaine at a young age.

According her upcoming memoir, "High on Arrival," due out Wednesday, her father had sex with her on the eve of her 1979 wedding to Jeff Sessler, a member of the Rolling Stones' entourage. "On the eve of my wedding, my father showed up, determined to stop it," Phillips writes in the book, according to excerpts obtained by People magazine.

A heavy drug user at the time, Mackenzie was 19 when the incident allegedly occurred. "I had tons of pills, and Dad had tons of everything too," she says. "Eventually I passed out on Dad's bed. ... My father was not a man with boundaries. He was full of love, and he was sick with drugs. I woke up that night from a blackout to find myself having sex with my own father."

As her life began to spiral out of control due to drug use, Phillips said the incestuous relationship became consensual. "Had this happened before? I didn't know," Phillips said. "All I can say is it was the first time I was aware of it."

Phillips entered rehab while on "One Day" and was eventually fired from the show in 1980 due to her drug use. She and John Phillips entered rehab together later, and she toured with him in a band called the New Mamas and Papas. "I was a fragment of a person, and my secret isolated me," she writes in the book. "One night Dad said, 'We could just run away to a country where no one would look down on us. There are countries where this is an accepted practice. Maybe Fiji.' "

Before John Phillips' death in 2001, Mackenzie confronted him about the abuse, saying to him, "We have to talk about when you raped me." Her father reportedly replied, "You mean when we made love?"

She also claims in the interview that Rolling Stones singer Mick Jagger cornered her once and said, "I've been waiting for this since you were 10 years old."

Phillips was arrested in 2008 at Los Angeles International Airport on suspicion of cocaine and heroin possession. She later pleaded guilty to one count of cocaine possession, for which she was ordered to enter a drug rehab program.