Carrie Underwood sang “Little Drummer Boy” by herself. Then she asked one more singer to join her.

Most singers would be happy with a finished take of a classic. Carrie Underwood heard hers and felt something was missing.

Carrie is one of the biggest voices in country music. In 2020 she put out her very first Christmas album, “My Gift.” It came out on Sept. 25, 2020, with 11 songs, and one of them was “Little Drummer Boy.”

She recorded that song on her own at first. But according to the Associated Press, as she listened back to it, one person kept coming to mind. So she decided to ask that person to sing it with her.

She wasn’t sure it would work, either. As she told the AP: “I told everybody, ‘This might not even work. This might be a terrible idea.'”

The singer she wanted was her son Isaiah. He was 5 years old.

Isaiah is the older of the two boys Carrie shares with her husband, retired NHL hockey player Mike Fisher. Carrie already knew how he felt about music. “(Isaiah) loves to sing. He loves music. He definitely has that passion,” Carrie said.

So she simply asked him. “I asked him, ‘Would you ever want to go in and sing with Mommy?’ He said, ‘Yes,'” she recalled.

In this AP interview, Carrie talks about how her son ended up on her Christmas record, and it’s lovely to hear it from her.

Carrie tells the AP about her little duet partner

Carrie didn’t leave him alone in there. She stood in the recording booth with Isaiah, cheering him on and reminding him of the next words.

He gave it everything. Carrie told Entertainment Tonight that “he’s throwing his hands in the air and just so expressive when he was singing it.” “He remembered the lyrics and he sang it with his whole heart,” she told PEOPLE TV.

“(And) he went in and he did such a great job,” she added to the AP.

Hearing it back hit her hard, in the best way. “When I first heard it back I was laughing and crying at the same time,” she said. Later she put it like this: “I was laughing, and I was crying, and it was just very overwhelming in a good way.”

Entertainment news shows picked up the story too, and this report on Isaiah’s singing debut is a fun quick recap.

A news report on Isaiah’s singing debut

Then came a moment for the whole family. They all piled into Carrie’s SUV to listen to the finished song. “We went in the car and Isaiah got to hear himself back for the first time,” she said. “It was just a great moment for all of us.”

Carrie’s pride came through when she talked about it. “I was so proud of him, just for giving it his all and the love in his heart because he does love Jesus,” she said.

Now you can hear exactly what the family heard in that car. Listen for the little voice that joins in on the classic.

Carrie and Isaiah sing “Little Drummer Boy”

Fans got a peek behind the scenes later that year. Her TV special, “My Gift: A Christmas Special From Carrie Underwood,” streamed on HBO Max in December 2020 and included a look at the recording.

Isaiah is 11 now. He was just a little guy when he stepped into that booth with his mom.