Anjelica Huston decided to leave Ryan O'Neal after he allegedly beat her because she listened to advice from her 13-year-old half-sister.
The 63-year-old actress has revealed she turned to her younger sibling Allegra because she felt she had nobody else in the world to talk to after she leaving then-partner Jack Nicholson, 77, for the 73-year-old actor, who she claims used to hit her.
Recalling an incident in the late 1970s when Ryan allegedly struck her, she said: "He turned on me, grabbed me by the hair, and hit me in the forehead with the top of his skull.
"I saw stars and reeled back, half blind, I ran away from him, upstairs to a bathroom."
She then explained Ryan turned up at the bathroom with a security guard and she allowed him to enter the room.
She added: "No sooner had I complied than Ryan was in the bathroom, batting me about the head with open hands. Then, abruptly, he left. I realized I had no one to turn to.
"I had given up my friends when I was with Ryan; they were too close to Jack, and I didn't want them to know what was going on.
"The next morning, with Allegra in the passenger seat of my car, driving on the Pacific Coast Highway, I asked her, sobbing, 'What shall I do, Allegra? What can I do?' She looked over at me cooly. She was 13 years old. 'Leave him,' she replied."
The 'Addams Family' star admits she later "regretted" leaving Jack - who she lived with on and off from 1973 to 1990 – for Ryan in the late 1970s because she "hated causing him pain", and on reflection she thinks her decision was "ridiculous".
Recalling the moment she told Jack she was leaving him, in an extract from her book 'Watch Me', printed in The Times newspaper, she added: "Jack's reaction was not to criticize or attack me. He was by turns confident and horrified; this event was sudden and surprising to him.
"For me, too. It came totally out of left field. I had no idea such a thing might occur. In truth, I found it quite ridiculous. How could this have happened?"
Following her affair with Ryan, Anjelica went back to Jack and he bought her a cottage close to his home on Mulholland Drive in southern California.
Anjelica went on to marry sculptor Robert Graham in 1992 and lived with him until his death in December 2008.