WATCH: Taylor Swift and Idina Menzel Perform “Let It Go” (In Costume)

Taylor Swift‘s 1989 World Tour has featured a host of amazing celebrity appearances, including Lisa Kudrow, but her latest guest performance tops them all.

For most people, Halloween marks the transition point from fall to the holiday season. And Swift set off an eternal winter when she performed ‘Let it Go’ with Idina Menzel (the voice of Elsa in Frozen) in full costume. Menzel was, of course, dressed as Elsa and Swift was… Olaf.

WATCH Taylor Swift and Idina Menzel Perform ‘Let It Go’:

“Frozen totally happened tonight,” Swift wrote on Instagram. “And 55,000 people sang ‘Let It Go’ so loudly, it nearly took my breath away.”

Menzel was also beyond excited about the performance: