On the eve of a world tour -- -- Europe, Asia and Australia -- to celebrate her brothers' -- THE OSMONDS -- 50th year in the business, MARIE OSMOND sits down with KEVIN FRAZIER to tell him she is at peace -- and that she has lost 45 pounds!

"It is not that I am skinny, but it is nice to be back in my jeans," Marie admits. "I feel healthy and my kids are proud of me."

The only Osmond sister, Marie reiterates what she told ET early on: She didn't lose the weight to look good, but for health reasons. She lost her father, mother and grandmother to heart disease, and she believes she was a ticking time bomb.

"My son came to me and said, 'Mom, you have to lose it.' It was very touching to me. The fact that I am a single parent made me reevaluate."

Marie lost a majority of the weight during her tenure on "Dancing with the Stars," but she explains that she was also on NutriSystem® at the time -- and continues to be.

"Everybody says you lost the weight from 'Dancing with the Stars.' Everybody was dancing and didn't lose that much. It was NutriSystem, exercise and the motivation of my children," she states.

Dropping from a size 10/12 to a 2/4, Marie says she has bought a whole new wardrobe, because none of her clothes fit, but she would never want any woman to "have" to do it.

"[The weight loss] is not why I am happy," she explains. "I made a lot of serious decisions in my life before I lost the weight. I think it is important to be at peace in your life."

Also on Marie's schedule is the upcoming "The 2008 Miss USA Pageant" [airing Friday, April 11 at 9 p.m. on NBC] and a week at the MGM Grand in Las Vegas with brother DONNY -- but no dates.

"Maybe when my five-year-old gets married, I will think about it," she jokes.