Chynna: I believe Mackenzie's incest story

LOS ANGELES, Sept. 23 (UPI) -- U.S. singer Chynna Phillips says she believes her older half-sister's claims that she had a nearly decade-long sexual relationship with their father.

Actress Mackenzie Phillips, who has battled drug addiction for years, said in her new memoir, "High on Arrival," that she had an incestuous relationship with her father, the Mamas and the Papas musician John Phillips, from the time she was 19.

Chynna, 41, told Us Weekly that Mackenzie, 49, first called her on the phone and told her about the relationship in 1997, 11 years after it ended. John died in 2001.

"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 recalled. "And she went on to tell me that she had had an incestuous relationship with our dad for about 10 years. ... Somebody could have dropped a piano on my head and I probably wouldn't have felt it. ... But I knew it was true. I mean, who in their right mind would make such a claim if it wasn't true?"

She added that the allegations deeply saddened her.

"A part of me died when I found out," Chynna said.