From mum to mom!

After Us Weekly exclusively revealed Jessica Simpson's unexpected second pregnancy in November, the Fashion Star mentor and mom to 8-month-old daughter Maxwell kept a low profile, neither confirming nor denying the news. But now she wants the whole world to know.

On Wednesday, Dec. 26 -- one day after confirming the pregnancy on Twitter with a photo of "Big Sis" Maxwell -- Simpson, 32, gushed about her second bundle-of-joy in a newly released Weight Watchers commercial.

"This year is all about new beginnings for me," she says in the ad. "I lost over 50 pounds on Weight Watchers and did not have to be perfect to do it. Being healthy has become a part of who I am -- which is great timing, because I'm having another baby."

The little boy or girl will be the second child for Simpson and fiance Eric Johnson. The pregnancy "definitely wasn't planned," a pal told Us, but the singer "loves being a mom" and "is overjoyed."

Indeed she is. "I feel like I'm on top of the world!" the Weight Watchers spokesperson says in her new commercial.

"Congrats to Jessica Simpson, Eric and big-sister-to-be Maxwell!" the company tweeted Tuesday, Dec. 25. "Your WW family is so thrilled for you. What an amazing year you've had!"

This article originally appeared on Usmagazine.com: Jessica Simpson Talks Second Pregnancy in New Weight Watchers Ad: It's "Great Timing"