Joaquin Phoenix and Rooney Mara have welcomed their first child, a baby boy.
The couple have named their son after Joaquin's brother River, who tragically died in 1993 from a drug overdose.
Rooney, 35, had previously not confirmed her pregnancy but had been seen with a baby bump over the summer.
The happy news was announced by Victor Kossakovsky at a Q&A session at the 2020 Zurich Film Festival following a screening of Gunda, a film which Joaquin, 45, worked on as executive producer.
Apologising for Joaquin's absence at the festival, Kossakovsky said: "He just got a baby, by the way, his name was… a beautiful son called River, so he cannot promote it now."
It's thought that baby River was born a month ago.
Rooney and Joaquin met when they worked together on the 2013 film Her.
But they didn't start dating until three years later.
They have also starred in Don’t Worry, He Won’t Get Far on Foot, Dominion and Mary Magdalene together.
The couple confirmed their engagement in May last year but are yet to get married.
Academy Award winner Joaquin said he initially thought Mara 'despised him'.
"She's the only girl I ever looked up on the internet," he told Vanity Fair last October.
"We were just friends, email friends.
"I'd never done that. Never looked up a girl online.”