Nicole Richie Guest Stars on 'Chuck,' Tells Costars Being a Mom Is "Best Thing Ever!"

First Lindsay Lohan on Ugly Betty, now Nicole Richie on Chuck...looks like professional behavior on set is the new 'in' thing amongst reformed It Girls. "Nicole came in and from day one was uber-professional [and] dedicated," says Zachary Levi, star of the NBC show Chuck.

Nicole wasn't the only one to make a guest appearance on set. Her seven-month-old daughter Harlow Winter Kate Madden was there "maybe every day," according to Zachary. "Such an adorable little baby!" he exclaimed. "I wanted to eat the baby. Is that wrong?"

While Harlow was busy fighting off her mom's cannabalistic co-star, Nicole was kicking butt as a former hot cheerleader on camera. "Nicole Richie is playing a super-villain and has a pretty bada** fight/shower sequence with Yvonne [Strahavoksi] where they're attacking each other with pipes and plumbing," says executive producer Josh Schwartz.

Yvonne says working with Nicole was "great fun. We got to kick each other's a**es, and we had a lot of fun doing it!" She added, "[Nicole] did not miss a beat in the fight scene!"

Between takes Yvonne spoke to Nicole about her new role as mommy: "She's loving being a mom. I asked her what it's like and she said, 'It's great. It's the best thing ever!'"

We're glad Nicole is taking to motherhood so easily, but wait til little Harlow hits her teen years, then we'll see if Nic still thinks it's the best thing ever...