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Jessica Simpson, Weight Watchers Ad

Courtesy: Weight Watchers

Jessica Simpson's svelte post-baby bod may not be around for much longer now that she's expecting baby No. 2 just seven months after welcoming daughter Maxwell.

But she's more than happy to sound off about her journey to getting back in shape: The Weight Watchers spokeswoman opens up about shedding her baby weight in a new ad campaign, which debuts on Christmas Day.

And, judging by photos snapped of the 32-year-old on set for the ad, that regimen seems to have worked like a charm: Simpson can be seen flaunting her banging figure while dressed in tight jeans, a relaxed plaid button-down and a slouchy belt.

Indeed, the star reportedly shed 50 pounds since she and fiancé Eric Johnson welcomed their daughter on May 1. But getting there took some serious commitment.

"When I had to go back to work, I had to bring my lunch because I didn't want craft services, which is definitely a new thing for me," she says in a behind-the-scenes video provided exclusively to E! News. "I'm more of a planner now—who knew?"

Staying on track became a top priority for Simpson, who notes that "I really had to make time to keep my workout routine…It's just an hour—there are ways to balance that."

With a new baby at home and another one on the way, Mama Jess is gonna be putting those balancing skills to the test!

For more about Jessica's post-baby weight loss, tune in to E! News tonight at 7 p.m. and 11:30 p.m.