Taylor Swift is almost done with her five-night stand at London's O2 Arena -- but she's not done bringing special guests on stage!

Swift invited Emeli Sande to join her Monday (Feb. 10) for a duet. They sang the British singer's hit 'Next to Me,' off her best-selling U.K. album, 'Our Version of Events.' Sande won big with the album at the 2013 Brit Awards -- and met Taylor there too!

Swift recounted how they got together by way of introducing Emeli to the crowd. "Do you remember the Brit Awards last year? I had a great time ... for a lot of reasons, but one of the most important reasons was that I got to meet one of my favorite artists," Taylor said. "And then she was so nice, you guys, she was so nice. And then I got to watch her absolutely clean up at the Brit Awards last year."

Taylor continued, "Then I just got the idea, 'What if she might come out and sing a song at the O2 for you?' London, what would you say if I told you Emeli Sande was here?"

The crowd cheered loudly and out came Emeli, with a smile as big as her voice. Taylor was as thrilled as the surprised audience members were, and later shared her delight with her followers on Twitter and Instagram:

During Swift's shows at the Arena last week, she was joined by Ed Sheeran and up-and-comer Sam Smith -- and also bum-rushed by an overly enthusiastic fan.

Tonight (Feb. 11) is T. Swizzle's fifth and final show in London, and she's clearly getting nostalgic already. She posted this cute photo collage of Swifties on Instagram yesterday with the heartfelt caption, "Oh my God, please never leave me."