Melissa Joan Hart has spilled the beans behind her 40 pound weight loss since giving birth to her third child in late 2012.

The 37-year-old actress revealed that she gained 60 pounds while carrying baby Tucker. However, she's says that Nutrisystem helped her shed the extra pounds. Now, the "Melissa & Joey" star told Entertainment Tonight that she feels "pretty amazing" in her new, slimmer body while on set to film a commercial wearing a swimsuit.

"I felt prepared. I was confident," she said while rocking a one-piece blue bathing suit. "I don't wear bikinis even when I go to the beach, so when I put it on in front of the cameras and all these people, and my husband showed up -- it's nerve-wracking but the feeling is very satisfying."

Back in December, the mother of three confessed, "I was so sick of things not fitting properly," to Us Weekly.

Since going on Nutrisystem last February, the former "Sabrina the Teenage Witch" star told Us Weekly that she has "lost three jean sizes, and all my baby weight and then some." Instead of setting a specific goal, she says, "I just wanted to put something on and be like, 'okay, good,'" she confessed. "I have been able to forgo the Spanx...and its been really nice."

She also revealed that she took her time working off the weight.

"For me, it was important to bond with my child, as opposed to 'lose the weight.' So I waited until I was ready, and I knew I had the time, and then I made it a priority that I would eat well," she said.

Now, the actress says she loves being fit.

"I could live like this," she said. "I love where I'm at and I feel amazing."

She also gushed about her supportive and disciplined husband, Mark.

"He is the guy who is disciplined," said Hart. "His whole thing is stick to it, be healthy, be fit and he does it for me ... I had three babies for him, but I also wanted to look fantastic into my 40's."

Watch the interview below.