Sunday’s iHeartRadio Music Awards teased a surprise during Madonna’s performance, and a surprise she did deliver: Taylor Swift turned up to play acoustic guitar on Madonna’s new single, “Ghosttown.” With the duo starting side by side on stools, the number began as an intimate, light-some-candles-and-sway ballad and turned into an electrifying meeting of the souls — specifically the souls of the biggest pop star of the moment and the biggest pop star of all time. Not just anyone can book Taylor Swift as a backup guitarist, after all.

Both singers posted joyful reactions on Instagram after the performance:

My new favorite guitar player! Thank you Taylor! Just you and I in a #ghostown ❤️#rebelhearts

A photo posted by Madonna (@madonna) on Mar 29, 2015 at 8:03pm PDT

I might be okay but I’m NOT FINE AT ALL. #MyFangirlLife #MadonnaAndTaylor

A photo posted by Taylor Swift (@taylorswift) on Mar 29, 2015 at 8:47pm PDT

Madonna reappeared shortly thereafter to present Swift with Song of the Year, which she won for “Shake It Off”: