In her new memoir High on Arrival, actress Mackenzie Phillips reveals how she had a 10-year affair with her father, musician John Phillips of the '60s band the Mamas and the Papas.
And in the new issue of Us Weekly (on newsstands now), her half-sister Chynna Phillips of the hit 90s group Wilson Phillips shares her side of the sad story.
Chynna, 41, tells Us Weekly she remembers getting the call from Mackenzie, 49, in 1997 — 11 years after the affair had ended — while she was between flights at LaGuardia Airport in New York City.
"She said, 'I don't know why, but I just really felt the need to call you and tell you something that I think you need to know,'" Chynna tells Us Weekly. "And she went on to tell me that she had had an incestuous relationship with our dad for about 10 years."
When the affair began, John was married to his third wife, model Genevieve Waïte. Chynna's reaction, naturally, was complete shock.
"Somebody could have dropped a piano on my head and I probably wouldn't have felt it," the singer tells Us Weekly. "But I knew it was true. I mean, who in their right mind would make such a claim if it wasn't true?"
She says the news sent her into "a deep, deep sadness and depression for about 10 days. A part of me died when I found out."
See today's top celeb news photos
In her book, Mackenzie — who, in 2008, pleaded guilty to one count of felony cocaine possession and agreed to enter an 18-month drug deferment program — also claims she and her father did drugs together. (She even tells Oprah Winfrey in an interview Wednesday, "My father shot me up for the first time.")
Chynna confirms to Us Weekly, "They were both doing drugs together.
"After long nights of heroin use, she's claiming that she once woke up and that my father was on top of her having sex with her," Chynna tells Us Weekly. "Was he actually raping her? I don't know. Do I believe that they had an incestuous relationship and that it went on for 10 years? Yes."
For more on the sad tale — including how a "disgusted" Chynna tried to distance herself from Mackenzie, why she eventually decided to stand by her half-sister and Mackenzie's lifelong struggle to stay sober — pick up the new Us Weekly today!
Sign up for Us Weekly's free, daily newsletter and never miss breaking news or exclusive stories about your favorite celebrities, TV shows and more!
For access to all our exclusive celebrity videos and interviews – Subscribe on YouTube!