Credit: Jason Merritt/Getty Images Photo: Melissa Joan Hart at the Premiere of What To Expect When You're Expecting in Hollywood, California on May 14, 2012

Melissa Joan Hart is a mom of three (feel old yet?), but that's not stopping her from being in amazing shape.

The 37-year-old actress and her husband Mark Wilkerson have three sons, 8-year-old Mason, 6-year-old Brady, and 1-year-old Tucker. We'll do the math for you — that's three babies in eight years! So how is Melissa looking so fab?

She credits the weight loss to Nutrisystem — the meal-delivery weight loss program. After gaining 60 lbs. while pregnant with Tucker, Melissa, ahem, explains it all, in the video below — she lost 40 lbs. on the program!

Check out the video to see Melissa's post-baby bod and to hear her chat about her weight loss. Doesn't she look incredible in that blue bathing suit? Sound off in the comments!

Credit: AOL Photo: Melissa Joan Hart Reveals Her 40-Pound Weight Loss! (VIDEO)