Christina and Jimmy showed up in costumes at an NYC subway terminal Wednesday and filmed their surprise performance for a 'Tonight Show' episode slated to air Thursday night. The pair teamed up for a couple tunes ... including George Michael's "Freedom! '90" and her 2002 hit, "Fighter."
The crowd was diggin' it, though they didn't seem all that surprised it was Christina and Jimmy. That voice and face are instantly recognizable. Watch ... even after the big reveal, the crowd played it off like they knew all along. They kept jamming, and fans kept clapping. A good time was had by all.