The couple performed Bryan's single "I Don't Want This Night to End" during Swift's concert in her hometown of Nashville, Tenn. on Thursday.
"You must have known that I wasn't going to show up here without a surprise for you," she told the crowd.
"This one's a really really good one. I think you're really really going to like it. 'Cause this is an artist that everybody really really really likes."
Are you really really tired of that word yet?
According to Swift, the performance changed her life. At least that's what she told her Twitter followers after the show.
Swift has teamed up with several other acts during her Red Tour, including Tegan and Sara, Cher Lloyd, Ed Sheeran, Jennifer Lopez and Sara Bareilles.
Nashville. That show was life changing & you were PERFECT. Thank you to @LukeBryanOnline, who came out and SLAYED. Never going to forget it.— Taylor Swift (@taylorswift13) September 20, 2013