Taylor Swift Joins B.o.B at Z100 Jingle Ball (VIDEO)

Taylor Swift surprised the crowd at NYC's Z100 Jingle Ball on Friday night (Dec. 7) when she came out onstage to perform with B.o.B. Although both were billed separately on the lineup, Swift joined Bobby Ray for a performance of "Both of Us," a track off the rapper's sophomore album Strange Clouds.

"I just had a record that was good and I thought, 'Let me just play this for her and see of if she likes it.'" B.o.B. told VIBE last month of how the collaboration came about. "I played ["Both Of Us"] for her and before the verse even dropped, her eyes were watering up. She was like “Yes, I wanna be a part of this song.” And the rest is history."

Watch the the two perform together at Madison Square Garden below.