Jan Gaye - who married the soul singer in 1977 and filed for legal separation two years later, though they remained in an on/off relationship until his murder in 1984 - claims the 'Love Story' actor approached her table at a Beverly Hills lunch and rubbed his penis against the bag of her head through his clothes, all while conversing with the 'What's Going On' singer.
She recalled: ''He arrived at our table and shook hands with Marvin, who introduced him to me. I was thrilled.
''The thrill took a different turn though when O'Neal stood behind my chair and pressed himself against my neck that was covered over by my long, wild hair.
''He made his move with great subtlety, but there was no mistaking the feel of his penis against my neck.
''As he spoke with Marvin, he kept pressing ever so slightly. I had a funny smile on my face. I didn't know what to say or do.
''So I did nothing. When he left, I didn't share the experience with Marvin. I was afraid it would only lead to a fight.''
Jan, 59, explained that earlier in their visit to the eatery, Marvin noticed Candice Bergen and described her as ''gorgeous enough to stop traffic''' but then accused his wife of having ''sexual designs'' on her, but she told him she was astonished by her stunning looks and compared her feeling to how her husband felt when he first saw Ryan in the restaurant.
In an extract from her autobiography 'After the Dance: My Life with Marvin Gaye' obtained by DailyMail.com, she said: ''During that same lunch we noticed Ryan O'Neal ... it was Marvin who seemed obsessed. He couldn't stop staring. I didn't see a physical attraction, but merely fascination.
''I told Marvin, 'If I can see that you're not sexualising Ryan - just admiring him - then I hope you can see that I wasn't sexualising Candice. Beauty is captivating.''
Ryan, 74, has denied Jan's account of what happened.
He said: ''I've never met the woman.''
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