Rose Byrne has given birth to her first child

The 'Bridesmaids' actress and partner Bobby Cannavale welcomed son Rocco into the world on February 1, the actor has revealed.

Speaking on 'The Late Show with Stephen Colbert' on Friday (05.02.16), he said: "I had a baby on Monday, yes."

The 45-year-old star joked he has been comfort eating to get through the exhaustion of having a newborn.

He said: "You know, I didn't do anything. We [fathers] don't do anything and I'm so tired. I think I've gained 28 pounds since Monday.

"I mean, I'm not kidding you. Like, this jacket fit so well, like, last Thursday. But I've been eating so much."

Elsewhere in the interview, Bobby revealed his friend and "idol" Al Pacino had sent a special gift to welcome Rocco into the world.

He said: "It was so sweet ... it was a big cake made out of diapers.

"[He said:] 'It's for your boy'. "

The 'Boardwalk Empire' actor - who has a 20-year-old son with ex-wife Jenny Lumet - and his 36-year-old partner fuelled speculation they were expecting their first child in October after Rose was pictured with a blossoming bump under a loose-fitting dress.

The couple have been together for three years.