Skylar Grey Performs 'I Need a Doctor' with Karmin [Video]

Karmin got a surprise visit from Skylar Grey, who joined the YouTube duo during their acoustic performance of “I Need a Doctor” at Billboard’s Lollapalooza lounge in Chicago this weekend.

Nick sang the hook while Amy held down the rap verses before Skylar dropped in to sing the song she helped pen for Dr. Dre’s Detox.

Karmin has garnered millions of views online with their covers of Nick Minaj’s “Super Bass” and Chris Brown’s “Look at Me Now,” attracting the attention of L.A. Reid, who signed them to Epic Records.