(Cover) - EN Showbiz - Selena Gomez wanted to look "grown up" at the Billboard Music Awards, according to her stylist.

The 18-year-old actress and singer accompanied her boyfriend Justin Bieber to the prestigious music event on Sunday night.

The American star, who typically wears sweet and unassuming dresses, dazzled on the red carpet in a daring black cut-out Dolce & Gabbana gown, which also featured a sexy thigh-high slit.

Selena's stylist says the brunette beauty wanted to show her more adult side with the outfit choice.

"She wanted to look a little bit more grown up," Basia Richards told 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," she added.

Selena and her 17-year-old beau are currently on a romantic vacation in Hawaii.

The pair's break comes after Justin's incredible Billboard Music Awards sweep, where he took home six gongs, including best new artist. (C) Cover Media