The star, who looks fabulous in the revealing two-piece, has confessed it's the first time she's ever worn a bikini and was overwhelmed with tears of joy during the shoot.
"I used to eat chips and cookies and drink soda all day long," Kelly admitted. "I had to start making better choices.
"I indulge with pizza and cheese - I love Brie - and have cookies sometimes. But now, when I'm full I stop eating! It may have taken me 26 years to figure it out, but I've finally learned how to do it right."
Kelly attributes her transformation and newfound confidence to her dance partner on Dancing With the Stars, Louis Van Amstel.
"He made me eat turkey burgers and salads," she says. "Then I started losing weight and realised, 'Oh, it's true what they say: Diet and exercise really work!'"
Kelly opens up about the effect the media had on her self-esteem when she was taunted about her weight.
"I understand that being judged by others comes with the territory, but it broke my heart and ruined my self esteem," she says.
"It sets you up to hate yourself in a huge way. I was so angry about the things people said about me. I truly believe it's the main reason I turned to Vicodin and ended up in rehab three times. I just hated myself."
Now Kelly has a healthy outlook. Her latest weight-loss secret is a new excerise technique: "My girlfriends and I just started doing plyometrics.
"It's a killer - it hurts so much. But when you walk out of there, you're like, "I can't believe I just did that and my body looks this good."