Brooke Shields has looked fabulous for as long as we can remember, which is why it comes as no surprise that she still fits into those Calvin Klein jeans from her famous early-'80s ads.

"It's not pretty, but if I lie down, and I suck in, I can get 'em zipped up," Shields joked in an exclusive interview with FNM. "I did it once, and I proved something to myself," she added. "I'm not sure what."

All kidding aside, Brooke did look spectacular, so we just had to ask about her exercise habits. "I have to work at it," she admitted. "It doesn't come easily to fit into anything."

Watch the video above to hear about Shields' favorite exercises and dieting tricks for keeping slim. (And keep listening to find out what she did with those original Calvin Klein jeans!)