Back in July Bieber heard that Taylor covered one of his hits during a show in Toronto prompting the Canada native to take to Twitter and write "heard you sang BABY at your concert in TO. thank u for the love ... might have to come by and stop in on a show."
Last night the pop idol followed through surprising fans at Swift's L.A. concert at the Staples Center with a duet of Bieber's hit song Baby.
After the show ended, Swift tweeted "You think you've heard LOUD screaming in your life.. Then @justinbieber comes out and does a surprise song during your show. Woah. Unreal."
The duet was such a hit, Bieber hinted at another round saying: "@taylorswift13 we should do that more often. :) great show! #muchlove."
Swift will be in Los Angeles for three more shows for her Speak Now tour at the Staples Center this Wednesday, Saturday and Sunday.