How does Kim Kardashian keep her famous derriere looking so fab?

"I'm half Armenian, so the butt really comes from my dad's side of the family. It's a little bigger, so you do have to work out more," she tells Australia's Cosmopolitan magazine. "I do squats and lunges. I try to do whatever I can to work out. It's all real."

Though she's been plagued by plastic surgery rumors since her career began, the newly-engaged reality star insists that reports of "butt implants" are simply "ridiculous."

"I'm proud of my booty and it's all mine," she tells the mag. "I have not had cosmetic surgery. I tried Botox once, but I have not had my nose done or anything to my butt. No injections! I'm very happy with the way I am."

What does the reality star's fiance, New Jersey Nets forward Kris Humphries, 26, like most about Kardashian's body?

"I think he likes my lips and, obviously, my butt," she told Us Weekly in April.