Fans finally got the naked truth from Jake Gyllenhaal.

While on Jimmy Kimmel Live Thursday to promote his new film Brothers, Gyllenhaal, 28, teases about shedding his clothes with an A-list actress — and it's not Reese Witherspoon!

"[I'm] making a movie with Annie Hathaway, and we've been having a lot of love scenes in that movie," he said of the 2010 film Love and Other Drugs. "And we've been baring almost all of us… So, that's not been that bad, either. We were pretty much naked but for a merkin."

A merkin, he joked, is a device that "prostitutes used to wear when they shaved their pubic hair in the 16th century … because they thought they had crabs." He said his device is "a cover for your junk."

When Jimmy Kimmel asked what Anne Hathaway, 27, wore during their intimate scenes, he remained mum.

"Out of respect to Anne, I’m going to have to leave that up to her when she comes on the show," he said, but then revealed that "it's a similar sort of thing, but it has other functions."

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Merkins aside, Gyllenhaal proved his maturity at a press conference earlier that day when he talked about growing up because of the children in his life.

"I've learned so much from the kids in my life, and somehow they just become the center of your life and the way you look at things," he told reporters in reference to his niece Ramona and Witherspoon's children, Ava, 10, and Deacon, 6. "Obviously I exist in my girlfriend's world and my sister's world in a different way, but it's opened my heart and I feel much more grown up and want to be grown up as a result of it."

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