-- Taylor Swift's ended her "1989" tour in Tampa, Florida, on Saturday night, and one of her surprise guests was cooler than cool.
The "Shake It Off" singer invited actress Idina Menzel to the stage, and the duo performed "Let It Go" from the Disney movie "Frozen" while dressed in full "Frozen" costumes.
Menzel, who plays the voice of Queen Elsa in the movie, wore Elsa's signature blue gown, while Swift sported an Olaf the snowman costume.
Even Swift's back-up dancers got into the Halloween spirit, as they all dressed up as reindeer for the performance.
"Frozen totally happened tonight. And 55,000 people sang 'Let it Go' so loudly, it nearly took my breath away," wrote Swift.
The 24-year-old pop star also invited singer Alessia Cara on stage, and the duo performed Cara's hit "Here" together.
Swift later tweeted that both Cara and Menzel helped the "Blank Space" singer close an "amazing chapter" in her life.