One of the world's best a capella groups, Pentatonix, released their massively successful holiday album and only Et's Brooke Anderson was behind the scenes for the making of their original Christmas video.

After winning NBC's The Sing-Off competition in 2011, Scott Hoying, Mitch Grassi, Kirstie Maldonado, Avi Kaplan and Kevin Olusola sky rocketed to fame and then got to work spending an immense amount of time recording in the studio and performing in arenas.

Video: Pentatonix Sings the Et Theme Song

All that hard work has clearly paid off as their holiday album, That's Christmas to Me, has gone platinum and surpassed Beyonce to become the fourth best-selling album of 2014. The group also received their first Grammy nomination for Best Arrangement, Instrumental or A Capella for their Daft Punk melody.

And if they weren't hot enough, they were asked to perform on The Kennedy Center Honors, airing Dec. 30 on CBS, where they sang "That Thing You Do" for...