Billie Eilish wins Grammy for Song of the Year for 'Bad Guy'

Billie Eilish took home the Grammy for Song of the Year for "Bad Guy" -- she is only 18 years old

Pop-rock innovator Billie Eilish on Sunday bested a packed field to win the Grammy for Song of the Year -- which honors songwriters -- for her hit "Bad Guy."

The 18-year-old beat veteran acts Lady Gaga, Taylor Swift and Lana Del Rey along with newcomers Lewis Capaldi and Lizzo to take home the coveted honor.

She shares the prize with her older brother Finneas O'Connell, her primary creative collaborator.

The pair were gracious onstage, with Eilish telling her fellow nominees: "I grew up watching all of you."

"We just make music in a bedroom together," said O'Connell. "We still do that and they let us do that. (...) This is to all of the kids making music in your bedrooms today -- you're going to get one of these."

Eilish was among this year's most nominated artists with six nods, and is the youngest person ever nominated in all four of the top categories.

Best song was her second award of the night. She won earlier for best pop vocal album for "when we all fall asleep, where do we go?"

Before she released the album in March 2019, Eilish had already assembled a fervent online following for her bold, often haunting pop sound.

In August, Eilish became the first musician born in the 2000s to top the Billboard Hot 100, when she dethroned Lil Nas X, who spent a record-breaking 19 weeks at the top with viral hit "Old Town Road."

The artist named Billboard's 2019 Woman of the Year has also written and will perform the theme song for the upcoming James Bond film "No Time To Die."

"I feel like I'm not supposed to be here," she told E! television on the red carpet before the gala. "Life is weird."