Clear your calendars on December 12 because MTV, VH1, Comedy Central, CMT and MTV2 have paired up with T-Mobile for an unprecedented eight-hour live stream that will celebrate the year in a major way.

The cross-network event will kick off at 12 p.m. ET and play out across 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.

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.

Among the fanbases in contention: Katycats (Katy Perry), Rihanna Navy (Rihanna), Little Monsters (Lady Gaga), Swifties (Taylor Swift), Animals (Ke$ha), Directioners (One Direction), Beliebers (Justin Bieber), Barbz (Nicki Minaj), Hooligans (Bruno Mars), Lovatics (Demi Lovato), Team Breezy (Chris Brown) and Team Britney (Britney Spears).

But wait, there's more! Carly Rae Jepsen will reveal her top five moments of 2012. She'll be joined by performers Grace Potter, Canadian indie rockers Metric, English buzz act alt-J, country duo Thompson Square, folk duo First Aid Kit and country singer songwriter Dustin Lynch, who will perform a surprise duet. (Additional performers and celebrity guests will be announced at a later date.)

"The Big & Best of 2012: A Year End Celebration Presented by T-Mobile" will be hosted by MTV News' Sway Calloway, VH1's Carrie Keagan and CMT's Kourtney Hansen and 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 show will include everything from celebrity interviews to live music, a fan army competition, year-end countdowns and lists and a scavenger hunt through Times Square in New York.

The live stream will also feature live new episodes of some of Viacom's signature series, including Comedy Central's "The Colbert Report"; MTV2's "Guy Code"; VH1's "Big Morning Buzz Live" and "You Oughta Know"; MTV News' "RapFix Live" and "After Hours"; MTV Hive's "Live in Boston"; Buzzworthy's "Bigger Than the Buzz"; and CMT's "Live in Nashville," "Live@CMT" and "Concrete Country."

"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 and special editions of "Rapfix Live," "Big Morning Buzz Live," "You Oughta Know" and much more!