Fans at Tony Bennett's concert at the Wolf Trap National Park for the Performing Arts in Virginia were in for a surprise when Bennett's longtime friend and collaborator Lady Gaga appeared on stage to join the 91-year-old jazz legend for a few of their favorite jazz standards. Wearing a strapless Oscar de la Renta gown, Gaga performed such classics as "Cheek to Cheek" and "The Lady Is A Tramp" to a standing ovation from the crowd. Watch below!

Lady Gaga and Tony Bennett released their collaboration album, Cheek to Cheek, back in September 2014. The record debuted at number one on the Billboard 200 and went on to win a Grammy Award for Best Traditional Pop Vocal Album. The two are rumored to be working on another joint album and were spotted together at the Electric Lady Studios in New York City earlier this year. "There'll be just wonderful songs that she and I both like," Tony said. "The first one went way over a million, and it's still selling."

Are you here for another Gaga and Tony album? Let us know in the comments!