Kristen Bell says Jimmy Kimmel's newborn son is doing well.

Kristen Bell

Kristen Bell

The 'Frozen' actress filled in for the chat show host on 'Jimmy Kimmel Live' last week when Jimmy took time off to be with his family after his son was born with two defects in his heart.

She told Entertainment Tonight: "[They're] good. Everybody's home, everybody's nursing, everybody's gaining weight."

And Kristen, 36, revealed Jimmy's dad was hugely impressed with her hosting skills.

She said: "Right after the show he said thank you so much again. First, early reviews are in with an attachment from his dad which was a very long text saying how much his dad loved the show. So really if Jimmy's dad liked the show I feel like I don't even need to know if anyone else enjoyed it. I'm cool with just knowing Jimmy's dad enjoyed it."

Meanwhile, Jimmy has thanked fans for their "love and support" after he opened up about his son's heart operation.

The 48-year-old American television presenter announced his wife, Molly McNearney, gave birth to their child William on April 21, but the tiny tot had to undergo an invasive procedure within a matter of hours, which left the parents fearing the worse.

Posting a picture of his wife with their son - who is nicknamed Billy - and Jane, the star wrote: "sincere thanks for the outpouring of love & support - Dr. Jane is keeping a close ear on Billy, who is very well - XO (sic)"

William has since left the hospital to settle in at home with his family, and the funnyman has revealed his child is doing "great" following the operation and is doing "all the things" babies should do, including peeing on his mother.

He continued: "He's doing great. He's eating. He's sleeping. He peed on his mother today while she was changing his diaper. He's doing all the things that he's supposed to do."