Watch Paul McCartney Perform 'Get Back' With Alabama Shakes' Brittany Howard

Paul McCartney served as Lollapalooza’s headliner Friday night in Chicago, and the former Beatle had a special guest in the store to help him out during the encore: Alabama Shakes’ Brittany Howard, who joined McCartney for a rousing rendition of “Get Back.” The Sound & Color band had performed at the Chicago fest…