Mackenzie Phillips was on "The Oprah Winfrey Show" on Wednesday (September 23) to discuss her new book, "High on Arrival," and she candidly spoke about drug addiction and her alleged decade-long sexual relationship with her dad, late Mamas and the Papas singer John Phillips.

"This isn't exactly how I envisioned this going down," she told Winfrey, with tears welling up in her eyes, before reading a passage from her book where she recalls having sex with her dad for what she thinks is the first time. "I boxed it away. It started very early on in my life. And this was the mother of all difficult experiences. I was 17, 18. I wasn't a small child, but I'll tell you something, it was one of those things where you tell yourself, 'Don't look.' ... I felt so alone. And I think my father was not a bad man. It's kind of a testimony to what drugs and alcohol [do]."

After an initial sexual encounter when she was in her late teens, Phillips went on to talk about how that relationship continued. "Fast-forward, I'm on the road with my dad and it's 1981, maybe, and we're touring, and I begin waking up after drug-filled events with my pants around my ankles and my father sleeping beside me. And again: 'Don't think, don't look, just keeping going.' This happened over time. It didn't happen every day, but it happened enough times, many times," she explained.

Along with their sexual relationship, John and Mackenzie were also tied together through other demons. "I had tried drugs," she said. "I tried it when I was 11. I didn't start using cocaine until I was 15. I pilfered [my dad's] personal pharmacy. He taught me to roll joints when I was 10. He took out some pot from a shoebox and showed me ... and I became the official joint roller.

"I was probably 16 or 17, and my father shot me up for the first time, and I remember going up to my room," she continued. "He tied me off and put the needle in my arm and he missed the vein and my whole arm went numb. So I remember this particular time trying to shoot up in my ankle, but he walked in and he said, 'Ah, baby, you're not doing it right' [and then he talked me through it]. That's how I learned how to do it."

It took a very intense experience for Mackenzie to stop the relationship with her dad. In the late '80s, she found out she was pregnant and knew there was a good chance the kid was her father's.

"I became pregnant, and I was in a relationship with my son's father as well. But I came up pregnant, and I did not know who the father was," she said. "The implications, the reality of that ... I had an abortion, and I never let [my father] touch me again."

Despite the abuse, Phillips says she still loves her father. "I [told him on his death bed], 'Dad, we've been through a lot.' And I said, 'I would not be the woman I am had I not been your daughter, and I'm very proud of the woman I am,' " she recalled. "And I said, 'I love you and forgive you,' and writing this book, I wanted to earn the right to speak about forgiveness."

Although half-sister Chynna doesn't deny the allegations, Mackenzie said that her siblings are having a hard time with the book. Her stepmother released a statement disputing Mackenzie's claims. "As with any family coming and going public about incestuous abuse, people want to sweep it under the table," Mackenzie said. "But yes, my brothers and sisters definitely have a problem with this."