Chenoweth began the song, singing the part of Glinda, a role she originated on Broadway and received a Tony nomination for. She seemed surprised when Horn began belting the part of Elphaba, harmonizing beautifully with her and appearing very comfortable in front of the audience of 10,000 people.
At one point, Chenoweth exclaimed, "Holy crap. Harmony!"
After Horn left the stage, Chenoweth expressed admiration for Horn's talent and said to the audience, "That voice is teaching our young people."
Check out the recording of the duet below!