Kelly Clarkson debuted a slimmer figure at the 2012 Billboard Music Awards during her performance of Dark Side Sunday night, sporting a hot-pink cutout gown that showed off her weight loss.

The former American Idol winner Clarkson, 30, is seen in photos from the Billboard Awards in Las Vegas on Sunday night wearing a gown with a plunging neckline that showed off a svelte décolletage. Clarkson paired her look with her brown hair in loose waves and simple, natural-looking makeup. Last week, Clarkson was looking equally as slender for her appearance at ABC's Upfronts presentation in New York City.

According to Alicia Hunter, weight loss expert and author of The Accidental Diet: From Fugly to Fox, Clarkson appears to have lost about 40 pounds.

Her arms are a far, slimmed-down cry from her earlier picture and her face looks more defined too! She's also shed several inches from her waist, Hunter told The Hollywood Life. The dramatic difference in her arms and waistline could only have come from losing a lot of actual body fat, which needs to happen not only through a low-calorie meal plan, but also cardio.

Since her days on American Idol in 2002, Clarkson has been highly scrutinized by the media for her fluctuating weight, jumping up and down for years. However, the singer maintained back in 2009 that her weight is not a concern for her.

When people talk about my weight, I'm like, 'You seem to have a problem with it; I don't. I'm fine, she told Self in 2009. I'm never trying to lose weight -- or gain it. I'm just being.

Clarkson has reportedly been slimming down for the debut of her new NBC singing competition show, Duets, with Robin Thicke, Jennifer Nettles and John Legend.

Or perhaps her weight loss comes in light of her new relationship with Brandon Blackstock. In March, Clarkson was rumored to be dating the son of her manager, Narvel Blackstock, and stepson of Reba McEntire, according to US Weekly.

Before Brandon, Kelly had a really tough time with love, a source told Us Weekly. [Brandon] is just what she needed.

View the slideshow to see photos of Kelly Clarkson and her dramatic weight loss.