The new mom, 32, was all smiles on Monday when she sat down with Katie Couric on the debut of Katie, where she revealed her post-baby body.
"On my way to @katiecouric's show! I'm her very first guest - Wish me luck!! #WeightWatchers," she Tweeted before the big reveal, also sharing the photo above.
Just weeks after welcoming daughter Maxwell Drew with fiancé Eric Johnson on May 1, Simpson embarked on a weight-loss plan with Weight Watchers.
Announcing that she's lost more than 40 lbs. since delivering, Simpson told the talk show host, "My doctors told me [my pregnancy weight] was a lot of water, and when my water broke … All the weight did not come out with the baby. I had to stay focused on my diet. I want to be as healthy as I can because I'm a mom now."
Simpson adds that she is currently 10 lbs. from her pre-baby weight, so moving forward, "I set small goals for myself. I've lost weight every week, thank God, but I've worked really hard. I have to shoot a new season of Fashion Star."
A new outlook on food has helped.
"The only fish I ever ate was a fish stick," Simpson says, adding that she also loved chips, guacamole and queso. "Now I'm trying to eat fish."
She adds, "I definitely don't pick up the magazines. I definitely don't Google my name. I try to avoid it completely. But I subconsciously know the talk is going on. Every day it's a struggle for me. Weight Watchers is not intimidating. It's not a diet. It's a lifestyle."
Simpson, who admits she "put on more baby weight than I was planning," isn't ashamed of her former body.
"I have to separate myself from the world's expectations," she says. "I have to look inside myself. I want to be a role model."
The new mom gave fans a sneak peek of her new figure when she was snapped by paparazzi on Sunday.
"I think anybody who's gone through a pregnancy, after they have the baby, it's like, 'I need to do something about this,' " she told PEOPLE at the time. "For me, I really want to do something that is a lifestyle, because in the past, I've been known to yo-yo diet."
Even though Simpson is getting her body back now, that doesn't mean she's rushing to slip into a wedding gown.
She and Johnson "have not set a date," Simpson told Couric. "It won't be this year. We haven't had time. Maxwell has taken up all our time and I want a big wedding."
Of her hubby-to-be, Simpson gushes, "People call him the best dad in the world. He can do everything. He's just a very peaceful person."