Newly signed performing rap/guitar/piano duo Karmin got a surprise visit from singer Skylar Grey, who joined the YouTube sensation during an acoustic performance of Dr Dre‘s single “I Need a Doctor” at Billboard’s Lollapalooza lounge in the States this weekend. Nick sang the hook during this performance while Amy held down Eminem‘s rap verses before Skylar popped up to join in on her part – check out the video below.

Karmin has racked up millions of views online with their covers of Chris Brown’s “Look at Me Now,” and Lil Wayne‘s “6 foot 7” amongst others, which attracted the attention of L.A. Reid who signed them to Epic Records.