Dec. 18 (UPI) -- Carrie Underwood says her son Isaiah did "a great job" on their duet.
Underwood's "The Little Drummer Boy" features Isaiah's vocals and appears on her holiday album, My Gift, released in September. On The Kelly Clarkson Show, Underwood said Isaiah was excited to hear himself on the record.
"I had no idea what was gonna happen. He's never been in that kind of situation before," the star said. "I don't think he's even been in the studio with me ever before. I don't know if he knows what I do at all."
"I could hear his voice on it in my head when I was singing it in the studio. I just thought I'd ask him and see if he might want to," she added. "He did such a good job."
Underwood said Isaiah is "so proud" of their duet.
"He went to school and he's like, 'Hey, my song's out. Wanna hear my song?' They were, like, listening to it in his class," she said.
Underwood previously told People that working with Isaiah was "so great."
"When we recorded, I was able to be in the booth with him and encourage him and try to remind him what words were coming up next, things like that," the singer said.
"I got to listen to his vocals [get] put together and then listening to myself with him," she added. "I was laughing, and I was crying, and it was just very overwhelming in a good way. It's just very emotional."
Underwood and Fisher married in July 2010 and also have a 22-month-old son, Jacob.
"It was kind of once things started taking off. The thought of me going to Hollywood by myself, and I had never been on a plane before, it was very unlike me to just go for it," she said. "It was scary, so I definitely had a moment of 'What am I doing?' It's easier to stay home."