Mackenzie Phillips, troubled actress, daughter of legendary rocker John Phillips (of The Mamas and the Papas) and older sister of Bijou, revealed that she had a long-term incestuous relationship with her own father in a new book, High on Arrival.

"On the eve of my wedding, [at 19, to Jeff Sessler] my father showed up, determined to stop it," Mackenzie writes in her new novel. " I had tons of pills, and Dad had tons of everything too. Eventually I passed out on his bed... I woke up that night from a blackout to find myself having sex with my own father. Had this happened before? I don't know. All I can say is it was the first time I was aware of it."

And if that revelation wasn't disturbing enough, Mackenzie goes on to chronicle an almost 10-year relationship, in which the father-daughter couple talked about running away to be together.

"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...He was completely delusional. No, I thought were going to hell for this."

Mackenzie has wrestled with her demons for years, having been arrested for felony possession of cocaine and in and out of rehab at least 9 times. And, as she tells Oprah in an interview airing Wednesday, "My father shot me up for the first time."

Mackenzie's sister Chynna Phillips (of Wilson Phillips) tells Us about the first time she heard of the incestuous affair, 11 years after it had ended, in 1997.

"Somebody could have dropped a piano on my head and I probably wouldn't have felt it," the singer told the mag. "But I knew it was true. I mean, who in their right mind would make such a claim if it wasn't true?"

Chynna says that upon hearing the news, she went into "a deep, deep sadness and depression for about 10 days. A part of me died when I found out."

"Do I believe that they had an incestuous relationship and that it went on for 10 years?" she went on to say. "Yes."