If you're a fan of The Sing-Off, you're already familiar with this group.
Pentatonix won season three of the show back in 2011.
Since then, they've experienced major YouTube fame, currently amassing more than five million subscribers. (That sentence feels goofy, but it's too late now. Heh)
Here's the latest of their videos to go viral...
YouTube Description: [Official Video] Say Something - Pentatonix (A Great Big World & Christina Aguilera Cover)
Absolutely love it. Whattya think? Feel free to leave a comment below.