EXCLUSIVE: Melissa Joan Hart Is 40?! Inside the Fabulous Birthday Bash She Planned Herself!

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Melissa Joan Hart turned 40 years old on Monday and ET was with her over the weekend to help celebrate the milestone birthday with a party she planned herself!

"There's something about gaining a little bit of wisdom, a little bit of self-confidence, a little bit of 'I don't give a crap' kind of, you know?" Hart told ET's Jennifer Peros.

WATCH: Melissa Joan Hart Remembers Her Wild Days

Fifty guests gathered at Winvian Farm in Connecticut on Sunday to honor Hart at the blue and white-themed event that featured a three-tier chocolate and vanilla cake and a surprise guest entertainer -- Hart's husband of 13 years, singer Mark Wilkerson.

The Course of Nature frontman dished to ET about the secret to their lasting marriage.

"We committed, when we first got married, that we weren't going to work at the same time," Wilkerson explained. "We had a couple of times where we were both working and it was hell, so we won't do that again."

But Wilkerson wasn't the first to get Hart's heart racing. Long before the couple fell in love and had their three children (Braydon, 8, Mason, 10, and Tucker, 3), Hart had a thing for Ryan Reynolds.

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"We worked together and there was a moment where we maybe could have had a relationship, but I was in a relationship with another boy, so I stayed true to that one," Hart explained.

It's hard to believe the actress' age, considering she was just a teenager when she broke out on Nickelodeon's Clarissa Explains It All, but she's feeling fabulous at 40 in large part thanks to the 40 pounds she lost on Nutrisystem! Watch the video below to hear more about her weight-loss journey.