The two UK singers came together for Sam Smith's hit single, "Stay With Me," in Manchester.
Hip-hop dancers Mia and Car Car from Maryland performed a fierce routine to a mashup of Danity Kane's "Lemonade" and Fifth Harmony's "Bo$$."
Before her four hour-long co-hosting gig on "On Air With Ryan Seacrest," the 24-year-old appeared on "Good Morning America" and performed "Shake It Off," "Out of the Woods," and "Welcome to New York" on Thursday.
The 24-year-old also discussed the song selection process for her fifth studio album "1989" during her "On Air With Ryan Seacrest" takeover on Thursday.
The "Shake It Off" singer knows how to keep her fans happy ... and always guessing.