Taylor Swift Duets with Nelly on Stage in St. Louis

During Taylor Swift's last tour, she often welcomed other performers on stage for duets, and she continued the tradition Tuesday night in St. Louis, Missouri....as Nelly joined her on stage for a performance of his new single "Hey Porsche."

The fans went wild when Taylor introduced the rapper, saying, "I'm just curious. What would you say if I told you that Nelly was here?" He then appeared at the top of the stairs on the stage, singing "Hey Porsche."

"St Louis, you were insanely loud and fun and amazing," tweeted Taylor. "Thanks for coming, guys. And a huge thank you to @Nelly_Mo for coming out to sing!!!" Nelly tweeted, "S/O to @taylorswift13 for rockin DaLOU!"

Back in 2011, when Taylor played St. Louis, she performed Nelly's hit "Just a Dream."