Jessica Simpson's Post-Pregnancy Slim-Down: She's Lost 40 Pounds in Four Months!

Jessica Simpson will make her national post-pregnancy reveal in front of millions on the premiere episode of Katie, Katie Couric's new talk show, on Sept. 10, and though she's not yet at her ultimate goal of 130 pounds, the star has shed some serious weight.

Life & Style has learned that the new mom has lost 40 pounds of pregnancy weight in just four months thanks to breast-feeding, marathon gym sessions and a personalized, no-starve Weight Watchers plan.

"Jess has been doing a lot of work on herself," an insider tells Life & Style. "And she'll gradually be showing her weight loss through Weight Watchers commercials over the next few months."

In fact, the singer and fashion mogul filmed her first commercial for the weight-loss company on Aug. 16. "She has met all her Weight Watchers goals and is overjoyed," a friend tells Life & Style. "She's so proud of herself."

Jessica recently opened up to USA Today revealing her struggles to get back in shape. "My body is not bouncing back like a supermodel," Jessica said, "I'm just your everyday woman who is trying to feel good and be healthy for her daughter, her fiancé and herself."

For more on Jessica's weight loss, pick up this week's issue of Life & Style, on newsstands now.