Credit: Matthew Symons/Coleman-Rayner

At 39 years old, model and actress Rebecca Romijn has never looked better.

The Thundercats star -- who gave birth to twins Charlie and Dolly in December 2008 -- showed off her impressive six-pack abs, lean legs and firm butt during a photo shoot in L.A. Friday.

After donning a skimpy gray and yellow bikini, the 5-foot-11 beauty changed into a mint green cardigan and matching daisy dukes for a second round of photos.

What's Romijn's secret to looking so good?

"I just have to keep working out. It's a goal every single day to break a sweat," the bikram yoga devotee told Us Weekly in May. "The goal is every day, but it usually ends up being about four times per week. And the class is 90 minutes each time, so that's good!"

Romijn -- who's been marreid to actor Jerry O'Connell since 2007 -- added that she "loves to eat," but during bikini season she tries to "eat lots of fruits and vegetables."

"I tend to eat a lot of salad in general," she told Us, "but in the summer I really stick with that."