Discussing the track Female, Nicole revealed that Keith asked her to lend her vocals to the track. "We have a studio in the house, and I was upstairs and he said, 'will you just come down?'"
"Of all songs to have her sing on, it was the right one," Urban added when talking to E! live on the red carpet.
For more red carpet action from the American Music Awards, check out our gallery featuring the best dressed stars!