Mackenzie Phillips' Half Sister Chynna Believes Incest Story

Sept. 25, 2009 -- Mackenzie Phillips is discovering what many who claim they are victims of incest have learned when they come forward -- their families don't always believe them.

The former child star of "One Day at a Time" returned to the Oprah Winfrey Show today to defend her decision to write her bombshell book "High on Arrival," in which she confessed to engaging in a 10-year consensual sexual relationship with her father, rock star John Phillips, the lead singer for the '60s group the Mamas and the Papas.

"It's been heartening and heartbreaking at the same time …with the way my family's reacting," she said about the response to her appearance on Wednesday.

Mackenzie, 49, spoke to Winfrey Friday by satellite. Her half sister Chynna Phillips, whose mother is actress Michelle Phillips, appeared live in Winfrey's studio. Chynna, an actress and singer who is now half of the Christian duo Chynna and Vaughn, said she wanted to appear separately so that her words would not be "convoluted."

Asked about her reaction to her sister's confession on the show, Chynna responded: "I was praying for her the whole time. It's very taboo. Many people were repulsed, horrified, for her to come out and talk about something no one wants to hear about, she had the courage. I'm proud of my sister."

When asked if she believed her older sister, Chynna laughed at first.

"How can the details be perfectly accurate, when you're on drugs?" she said.

"I do know there was a consensual relationship between my father and sister," she continued. "I've known that for about 12 years."