The big “Phillips Family Secret” Oprah’s been raving about is out. Former child star Mackenzie Phillips, best known for her role as Julie Cooper on the CBS classic One Day At A Time, has stunned fans and family by confessing she had a consensual sexual relationship with her rock legend father John Phillips for 10 years, CNN has learned.

Mackenzie says she was 19 when the “California Dreamin’” singer raped her just before she married Jeff Sessler in 1979.

“On the eve of my wedding, my father showed up, determined to stop it (the wedding). I had tons of pills, and Dad had tons of everything too. Eventually I passed out on Dad’s bed,” Mackenzie, now 49, writes in her new memoir High On Arrival, in stores today. “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,” Mackenzie claims.

“Had this happened before? I didn’t know. All I can say is it was the first time I was aware of it. For a moment I was in my body, in that horrible truth, and then I slid back into a blackout.”

The star has had a long history with drug use. Addiction cost her her starring role on the ’70s sitcom that made her a star. Most recently, in October 2008, she pleaded guilty to cocaine possession, following an incident during which she was arrested in August 2008 at Los Angeles International Airport. She was found carrying, “what appeared to be heroin and cocaine in baggies and balloons”

The incestuous relationship later became consensual after dad and daughter went to rehab together and began touring with The New Mamas and the Papas.

“I was a fragment of a person, and my secret isolated me. 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.’ He was completely delusional,” Mackenzie writes. “‘No,’ I thought, ‘we’re going to hell for this.’”

The affair ended in 1989. John Phillips died in 2001.