The Secret to Angie's Hot Post-Baby Body!

In her first public appearance since giving birth to twins Knox Leon and Vivienne Marcheline on July 12,  Angelina Jolie wowed throngs of waiting fans as she strutted her trim, post-baby body in a skin-tight, black strapless Versace dress at the NYC premiere of the Changeling on Oct. 4.

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By her side--her ever gallant partner Brad Pitt, who looked proud to escort the mother of his children down the red carpet.  Angie's amazing figure so soon after having twins would make even the most in-shape mother jealous. So how does she explain her killer post-baby body?

"Genetics," the actress told OK! at the Changeling's debut at the New York Film Festival. "Certain people are different in their shape. I'm breastfeeding and I think that's it. That's how your body naturally responds."

While it's true that nursing twins can help a woman burn 1000-1200 calories a day, it's not just Knox and Vivienne helping Angie shed the pounds. The actress, 33, admits running around with the kids is a big calorie-burner. As if to prove her point, just hours before the premiere, the doting mom took Maddox, 7, Pax, 4, Zahara, 3, to Lee's art shop.

"The kids were hyper and happy," says an eyewitness. Angelina is also adhering to a high-calorie, healthy diet. "She's learned the value of nutrition.  When she wants Pizza she'll have it. She eats in moderation."

The source adds, "After losing her mom Marcheline Bertrand died in January 2007 and looking so frail it was a wake up call."

Eating habits aside, it's clear that Angelina is settled and happy with her brood. "I feel great," she said at the premiere.  "I feel very happy that my kids are healthy."

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