Credit: Dimitrios Kambouris/

Heidi Klum, who was supposed to be acting as host of the Victoria's Secret Fashion Show, tells she was thrilled she actually got to walk down the runway Thursday night in New York City.

"I am excited," she told Us backstage shortly before walking out to cheers in a purple corset covered with a half gown with poufs of tulle. "I'm keeping it all together."

Just five weeks ago, Klum, 36, welcomed her fourth child, a girl named Lou, who is now in Los Angeles with the rest of her sibs (Klum's husband Seal is away in Australia performing).

"She's great," Klum told Us of her newborn. "I pre-pumped a lot of milk, left it in the freezer."

How has it been losing the baby weight?

"Every time it's the same," says Klum, who hopes to shed 20 more lbs. "You know, if you kind of gain 45 pounds, then it takes time to kind of go down again."

Former Project Runway champ Christian Siriano tells Us he is impressed with Klum's post-baby bod.

"She looked amazing!" he tells Us at an after-party at the Penthouse at Hotel on Rivington. "You're going to die. She looks -- oh my god! -- she looks so good!"

The Victoria's Secret Fashion Show airs Dec. 1 at 10 p.m. on CBS.