In Touch magazine has exclusively learned that the 20-year relationship between Gwen Stefani and Gavin Rossdale was in trouble before the couple even wed.

In an exclusive interview, a woman says she had a steamy sexual encounter with the Bush frontman at a 2002 Playboy Mansion party when he was already engaged to Gwen — and he kept texting her even after his wedding.

gwen stefani gavin rossdale

Gwen Stefani and Gavin Rossdale.

“He was beautiful and charming,” the party girl, who wishes to remain anonymous because of her connection to Hollywood, exclusively reveals. “He was with Gwen, but that didn’t stop him from hooking up with me.”

RELATED: Gwen Stefani Files For Divorce From Gavin Rossdale

“We spent a lot of time flirting,” the woman says. Eventually Gavin led her to one of the mansion’s Van rooms, which have padded floors where they started “fooling around.”

“[Gavin] said [he and Gwen] were having problems,” the woman tells In Touch. “I thought they were breaking up and that I had a chance.”

gwen stefani gavin rossdale

“I was head over heels in love with him,” she admits, adding that she was stunned when he wed Gwen later that year in London — and even more so when Gavin continued texting her for at least a month longer.

“I do feel bad for Gwen,” the woman says. “He’s just a cheater.”

For more details on Gavin’s infidelity, pick up the latest issue of In Touch magazine, on newsstands now!

Have a tip? Send it to us! Email In Touch at