VIDEO: Why Is Justin Bieber Kissing Ali Williams?

Ali Williams, 18, may not have been the biggest Justin Bieber fan when she and the teenage heartthrob locked lips on the music video for his new tune, "Mistletoe," but the college freshman was very "excited" to land the role as the Beib's female counterpart in the love song.

Williams' agent emailed her last minute about auditioning for the part, and video director Roman White was pretty secretive about who he was going to cast, but eventually Williams found out she'd landed the role that thousands of young Beliebers would die for, as it ends with a kiss from Bieber himself.

"I definitely admire him," Williams told MTV News after the video was released. "He's very successful in what he's doing. I wasn't too familiar with his music, but I was very excited to meet him, and I'm glad that I did," she said, also admitting that being a "household face" caught her a little off-guard. "I wasn't really prepared for all the stuff that was happening. I think that pretty much everyone has been pretty supportive."

The pop star was also "really easy to get along with, really polite," Williams added. "As far as the kissing, it was very professional. It's just a job." So Selena Gomez can rest easy at night.

Bieber's "Mistletoe" will be featured on the compilation Christmas album, Under the Mistletoe, which will also include singles from Mariah Carey, Boys II Men, Busta Rhymes and Usher. It hits stores on Tuesday, November 1.

Watch the music video here: