Demi Lovato, Kelly Clarkson, Pitbull and others will also hit the stage for the annual holiday concert at Madison Square Garden. By Christina Garibaldi Lady Gaga Photo: Ethan Miller/ Getty Images It’s time to get in the holiday spirit! On Friday (October 21), radio station Z100, with the help of pop star Demi Lovato , announced the lineup for their 2011 Jingle Ball concert. All you Little Monsters better mark your calendars, because Mother Monster herself, Lady Gaga , will be headlining the big event. The holiday concert will take place on Friday, December 9, at New York City’s Madison Square Garden. Lovato, who is also hitting the stage at Jingle Ball, helped announce the lineup at the official kickoff party at the A
