"When I was young my sister told me about this, It ruined my life and my relationship with my father," Bijou wrote in a Twitter post on Monday on an account that has since been removed. "Up till that point, I was a normal kid. I got good grades, loved my horse, was pretty innocent. I moved out to NYC, at 13."
According to Bijou the sexual abuse claims, which her half-sister details in her new book, "High On Arrival," lead to her own life spiraling out of control.
"Started doing drugs, did not talk to my Dad anymore…I was deeply f***ed up," she continued in a series of Tweets. "I'm 29 now, I've talked to everyone who was around during that time, I've asked the hard questions. I do not believe my Sister. Our father is many things, This is not one of them."
The 29-year-old actress went on to claim that Mackenzie's sexual abuse allegations were responsible for her damaged relationship with their father.
"My Dad and I made up when I was 20, a year before he died. I'm sad I lost those years with him, and I lost those years at home," she wrote in a final Tweet.
As previously reported on AccessHollywood.com, Mackenzie's former stepmothers Genevieve Phillips (Bijou's mom) and Michelle Phillips, have both spoken out against her claims. Half-sister Chynna Phillips has said she believes Mackenzie.
Related Content from AccessHollywood.com:
VIEW THE PHOTOS: Celebrity Parents Gone Nuts
PLAY IT NOW: How Does Mackenzie Phillips Feel About Her Father? (September 28, 2009)
PLAY IT NOW: Is Mackenzie Phillips Ready For Another Relationship? (September 25, 2009)