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Fergie revealed how she and husband Josh Duhamel keep things hot during the holiday season -- and it involves a sexy costume.

"One day every holiday season, he comes home and there's a naughty Mrs. Claus," the Black Eyed Peas front woman revealed to Ellen DeGeneres. "It depends how good he's being!"

A playful Fergie, 37, added, "It's a surprise. It's naughty and nice at the same time. It's super cute and fun."

Ellen also checked in on the thong she gifted Duhamel, 40, with the last time he was on her show. "It was too small," Fergie admitted. Ellen quipped back, "That's more information than we needed!"

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The Hollywood couple are known to send out holiday cards with a picture of themselves, but the singer confessed that they haven't mailed them out yet this year. "My husband orchestrates the whole thing and we're late this year because he's been filming a movie. He just finished Safe Haven with Julianne Hough and now he's doing You're Not You with Hilary Swank. I haven't been on the ball, so I'm waiting for him and we're going to have to do something last minute this year."