The impromptu collaboration took place during an episode of Legend’s Trailer Talk, a series that takes place behind-the-scenes of NBC’s The Voice.
The two superstars have a history together as they collaborated on Underwood’s holiday release, My Gift, on the song “Hallelujah.”
Having found stardom from a competition show herself, the seven-time GRAMMY winner also shared advice for The Voice contestants.
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Before taking the stage during Tuesday’s episode of The Voice finale to perform their Christmas collab, Underwood and Legend combined their voices on an unexpected tune.
“I was thinking it would be cool to do something country and you had a great idea,” Legend said.
“I know that this show is all about friendly competition amongst the judges and I feel like because you can sing anything, I would love to hear you voice on something country, so I think we should sing a Blake Shelton song and you should show him how it’s done,” Underwood revealed with a smile.
With Legend on keyboard, they went on to deliver a rendition of Shelton’s chart-topping debut single, “Austin.”
The goosebumps inducing performance even caught the attention of Shelton himself.
“Damn y’all…,” Shelton wrote in response to the performance.
The Voice finale returns on Tuesday evening to crown the winner.
The star-studded show will also feature performances by Jennifer Lopez, Carrie Underwood with John Legend, Alicia Keys, Walker Hayes, Ed Sheeran, Keke Palmer with Tori Kelly and Coldplay.