Stylist: Selena Gomez Wanted to Look "More Grown Up" In Sexy Cutout Dress

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The big wet smooch that Selena Gomez planted on her boyfriend Justin Bieber, 17, at the Billboard Music Awards isn't the only thing that has people buzzing about the 18-year-old star on Sunday night.

Gomez, who typically wears sweet and flirty dresses, sizzled on the red carpet in a skin-baring Dolce & Gabbana gown, which not only featured cutouts around her waistline, but also a thigh-slit in the front.

PHOTOS: What all the stars wore to the Billboard Awards

"She wanted to look a little bit more grown up," the star's stylist Basia Richards tells Us Weekly. "So we decided to make those custom cutouts to make it more fun yet mature."

But Gomez didn't leave her demure side totally in the dust. "To keep it age appropriate, we picked adorable red Giuseppe Zanotti heels with crystal bows," adds Richards.

PHOTOS: Selena's red carpet style

A day after her head-turning appearance at the awards show, Gomez and Bieber jetted off to Hawaii for a romantic getaway where she was snapped in a bright pink bikini top and daisy dukes.