Watch Kate Middleton perform with Tom Walker during Christmas concert at Westminster Abbey

The Duchess of Cambridge can add pianist to her royal resume.

During a Christmas concert that was broadcast on ITV in the U.K. on Friday, Kate Middleton accompanied Scottish singer-songwriter Tom Walker on piano when he performed a new song "For Those Who Can't Be Here" at Westminster Abbey.

The pairing came about after Walker performed at a charity event that the duchess was attending. When he was later asked to play at the carol service, Royal Carols: Together at Christmas, he offered to perform a previously unheard song, but didn't anticipate who would be joining him.

"So I sent [the song] over to the team and they absolutely loved it, and then a week later they came back and said, 'Um, would it be alright if the duchess played along with you?'" Walker told the BBC in an interview. "And I was like 'What?'"

Walker and the duchess got to work, rehearsing for some weeks. "She picked it up so well, it's really not easy to go from not playing with other musicians for like 10 years to jumping straight in with like a whole band you've never met and camera crews doing live takes that's being filmed in Westminster Abbey so I thought it just went so well," said Walker. "She's [a] very talented musician."

Ahead of the performance, Walker didn't disclose his famous bandmate to anyone — even keeping it a secret from his mom. "She was in floods of tears watching it on the telly," he said. "It was beautiful."

Royal Carols: Together at Christmas was organized by Middleton and Prince William and was attended by those who had spent time with the royal couple during recent engagements.

Watch the video above.

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