Jessica Simpson - Jessica Simpson Debuts New Post-baby Body

The fashion designer packed on the pounds when she fell pregnant with baby Maxwell last year (11), but she has shed a staggering 40 pounds (18 kilograms) in the months since she became a first-time mum.

And during an appearance on U.S. journalist Katie Couric's new talk show on Monday she walked on stage in a fitted black dress and patent leather pumps for the big reveal - as reported last week by WENN.

She said, "I've just had a lot of pressure on me to lose the baby weight. Today was actually one of my goals, getting here and just feeling comfortable in a beautiful dress, and I have to say I've achieved it, I feel beautiful today."

Simpson stopped short of announcing how much weight she had lost, but the reality star added, "I've lost enough weight to where I can pat myself on the back. It's a small child."

And the Irresistible hitmaker reveals not only did she find inspiration in her spokeswoman deal with weightloss company WeightWatchers, she has also been motivated to slim down for her upcoming season of Fashion Star.

She added, "I set small goals for myself... I've lost weight every week, thank God, but I've worked really, really hard. I have to shoot a new season of my show Fashion Star, so I want to be in all the pretty dresses and the designer gowns. I'm 10 pounds (4.5 kilograms) away from that, so, by the time we're shooting, I'll actually be smaller, which is exciting."

The 32 year old reportedly filmed her first commercial for the firm in August (12), and it is set to premiere on U.S. TV on Monday night.