Who knew you had to sneak sex at the Playboy Mansion?

Kendra Wilkinson, one of Playboy founder Hugh Hefner's three girlfriends on "The Girls Next Door," told US Weekly magazine that "I had to have sex every now and then, so I had to kind of sneak it."

While Wilkinson, 23, said she and Hefner were intimate at times, mostly she just saw him once a day in passing.

PHOTOS: Click for fun pics of Kendra Wilkinson.

Bridget Marquardt, on the other hand, stayed true to her (much older) man, according to Wilkinson.

"Bridget told me that she's been faithful all these years, and I was like, 'How the hell can you do that?' I had to have [sex] so I could feel my age, like a healthy human being."

Wilkinson described Hefner as more of a "sugar daddy" who kept close tabs on the girls, which made her "insane."

Wilkinson is now engaged to Philadelphia Eagles wide receiver Hank Baskett, and plans to marry him at the Playboy Mansion this summer.