Gibson's wife Robyn filed for divorce last month after 28 years of marriage, amid rumors that the actor had been dating 39-year-old Grigorieva.
And the Braveheart star unveiled his new relationship in public last week by taking his lover to a movie premiere in Los Angeles.
But Grigorieva, who previously dated Timothy Dalton, has come under fire from another former partner, businessman Alan Bergman, who claims the brunette dumped him as soon as she met the James Bond star.
He says, "She married a guy and they lived in a council house. I had more money and she left him and moved in with me.
"She then met Timothy Dalton at a party we went to, and within a week had moved in with him. She's a lovely girl but a bit of an opportunist."
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