Things got hot, hot, hot when Taylor Swift [1] welcomed her latest guests to the stage during her tour stop in St. Louis on Tuesday. The singer was joined by Nelly and a few of her BFFs, Haim's Este, Danielle, and Alana Haim. Together, the whole group performed Nelly's "Hot in Herre," [2] and his new single, "The Fix," and as Taylor explained on Instagram [3], she and her friends made up a dance together in the dressing room. She also shared a picture of herself singing alongside Nelly [4], writing, "Old friends. @derrtymo has come out to surprise the crowd on my last 3 tours. I absolutely adore him." Keep reading for all the best pictures from the group's performance, and then check out all the guests she's welcomed to the stage [5] throughout the 1989 tour.