"Hannah Montana" star Miley Cyrus and Taylor Swift are teaming up onstage -- for a performance of Swift's "Fifteen" at the Grammy Awards!

Swift, 19, and Cyrus, 16, decided to team up and sing Taylor's song from "Fearless" because it was so relatable. "They always love collaborations," Swift told E! News of the Grammy producers. "They always sort of suggest that you present them with a collaboration that you think makes sense. So Miley and I had always been talking about, 'When can we sing together? It would be so cool to sing together.' So we came to the Grammys and said, 'What about this song, 'Fifteen'? It really applies to us.'"

Swift is scheduled to perform again in L.A. on May 22 at the Staple's Center -- but people who want to see the country cutie in person needed to act quickly! The tickets to her concert sold out in two minutes.

Click here to view our photo gallery of 2009 Grammy nominees!