Mackenzie Phillips makes new claims about father's alleged abuse

For decades, Mackenzie Phillips said she lived with the pain of not being believed about her late father, John Phillips .

Then an unexpected letter landed in her hands – and changed everything.

Phillips opened up about a stunning letter from a longtime family friend that corroborated her claims of abuse by her late father during an episode of Valerie Bertinelli's podcast, " Get Naked ." Phillips recalled receiving the letter while working at Breathe Life Healing Center.

MACKENZIE PHILLIPS SHOCKS WITH 15-YEAR CELIBACY CONFESSION AS SHARON STONE, TERI HATCHER RETHINK ROMANCE "Head of HR comes in.

And he says, 'Oh, you got a letter.' And I said, 'Oh, wow.

It's probably fan mail.' Because, you know, we get fan mail there," she told Bertinelli.

"And I won't go into too much detail, but it was from one of the most credible sources you could ever know of a family friend saying that ... their husband observed something horrific when I was nine." "And I said, ‘Jeffrey’ – my brother, you know – 'I want to tell you.' He said, 'I don't want to know.' Nobody wants to know.

Nobody wants to know, you know," Mackenzie said.

"So I'm on my own again ...

I'm on my own in this nobody believes me." "Here's the thing is that I told the people – that said that I was lying – back then," she added.

"They already knew.

But I got this letter." Bertinelli asked Mackenzie how it affected her to find the courage to speak out only to have people not believe her.

MACKENZIE PHILLIPS SAYS SHE AND VALERIE BERTINELLI DRANK WINE, DID COCAINE DURING SITCOM BREAKS "Well, there's an element of protecting the legacy of The Mamas & The Papas ," she explained.

"I can separate the man from the music.