Harry Styles stepped in for James Corden on Tuesday night just hours before his Late Late Show aired.
As Styles came on stage to host the talk show, he announced that "our wonderful host James Corden had his baby today".
Ben Winston, the show's producer, said: "Congrats to the Cordens. And thanks to the incredible Harry Styles for stepping in literally at the last minute.
"What a performance with no prep!"
Corden shared the news on Twitter, writing: "Today we welcomed a beautiful baby daughter into the world. Both she and her mother are doing great.
"We can't stop smiling.
"Thank you Harry for stepping in to host the show at 2 and a half hours notice!"
Styles stepped in for Corden for the first time in May, and became a sidekick of sorts during the last few episodes of the season.
This time, he took the chance to congratulate Corden on his new baby, which Styles said he saw before coming to the studio.
"She looks a lot like James. Mainly because James looks like a giant baby," he said.
He also joked that his time as host would be a "one-time only" event... "unless CBS like what they see".
It is James and wife Julia's third child, after their son Max, and daughter Carey.