X Factor's Demi Lovato and 'Gangnam Style' sensation Psy have been confirmed to perform at the upcoming annual 'Christmas in Washington' event.

The special is set to air on December 21 on TNT and will also see live sets from the likes of legend Diana Ross, former 'American Idol' winner Scotty McCreery and 'Smash' star Megan Hilty.

President Obama and his wife, First Lady Michelle, are set to be in attendance and Late-night host Conan O'Brien will lead the telecast, which will come from Washington D.C.'s National Building Museum.

The event will also benefit the Children's National Medical Center.

Meanwhile, Lovato has been urging her followers on Twitter to vote for her X Factor USA acts to remain in the contest and shared a photo of herself on the phone (shown below) ringing in her own vote: "VOTING TIME!!!!!! Who says I'm not dedicated??!! LOVE YOU @CeCeMissXtotheO & @PaigeAva ❤"

Watch Lovato's music video for 'Give Your Heart A Break' here: