Justin Bieber Makes Carly Rae Jepsen's Year-End Faves: Watch Her 2012 Countdown Wednesday!

Carly Rae Jepsen pretty much ruled 2012, thanks to her inescapable viral smash, "Call Me Maybe." It was a song that catapulted the 27-year-old from struggling Canadian singer/songwriter to full-fledged pop superstar. After Justin Bieber heard the track and tweeted about it, there was no going back for Jepsen.

And, while there's been a lot to remember about this year. Jepsen recalled one of her top moments to MTV. "#5 would be Mexico City. In Mexico City, I was Justin Bieber's special guest at an outdoor event where there were 300,000 people in the audience and I was kind of speechless for the amount of them," she shared about one of her more memorable moments of the past 12 months. "And I thought 'How am I going to sing?' But, that was a really cool moment. We went up there sang 'Call Me Maybe' and they took it home with me."

To hear more from Jepsen as she reflects on her massive breakout year, you can tune into the "The Big & Best of 2012" live stream on December 12 at 12 p.m. The "Best of" special will also include appearances from Taylor Swift, who will tease her "I Knew You Were Trouble." video, and performances from Grammy-nominee Miguel and Unorthodox Jukeboxsinger Bruno Mars, among others.

Bruno Mars gears up for his "Big & Best" performance!

The cross-network event will kick off at 12 p.m. ET and play out across Viacom digital properties, including MTV.com, VH1.com, CMT.com and ComedyCentral.com, spotlighting the music, personalities and pop culture moments that defined 2012. The blowout party will include eight hours of live performances, celebrity guests and programming highlights from the past year.

Katycats, Little Monsters, Swifties and more go head-to-head in "Last Fans Standing." See how you can vote!

And you won't want to miss this event because 16 of music's most passionate fan armies will face off in head-to-head challenges across social media as part of Last Fans Standing. Only one group will emerge victorious and earn the crown of Best Fans of The Year. Voting is under way on MTV's Facebook page now, so be sure to help rack up points for your army before this round ends on December 12.

Hosted by MTV News' Sway Calloway, VH1's Carrie Keagan and CMT's Kourtney Hansen, "The Big & Best of 2012" will be broadcast live from MTV's legendary Times Square studio and on location in music venues in New York City, Boston and Nashville.

"The Big & Best of 2012: A Year End Celebration Presented by T-Mobile" goes LIVE at 12 p.m. ET on 12/12/12. Watch at bigandbestof2012.com for eight hours of live performances surprise guest appearances, prize giveaways, special editions of "RapFix Live," "Big Morning Buzz Live," "MTV News After Hours," "You Oughta Know" and much more!