Joaquin Phoenix and Fiancée Rooney Mara Welcome First Child River, Honoring Actor's Late Brother

Rooney Mara and Joaquin Phoenix made their red carpet debut as a couple at the 2017 Cannes Film Festival, and got engaged last year

No Joke(r) Joaquin Phoenix is a dad!

The Oscar-winning actor, 45, and his fiancée, Oscar-nominated actress Rooney Mara, have welcomed their first child together, a son named River after Phoenix's late brother who died in 1993.

Russian filmmaker Victor Kossakovsky, who Phoenix worked with on the dialogue-free documentary Gunda, confirmed the name of the couple's baby during an appearance at the 2020 Zurich Film Festival.

“He just got a baby by the way,” Kossakovsky said Sunday while speaking at the festival. “A beautiful son called River."

Rooney Mara and Joaquin Phoenix
Rooney Mara (L) and Joaquin Phoenix. Kevin Winter/Getty

Mara, 35, and Phoenix met on the set of the 2013 film Her and made their red carpet debut as a couple at the 2017 Cannes Film Festival. During the latter event, the pair were seen chatting and embracing warmly when Phoenix won the best actor award for his performance in You Were Never Really Here.

Rooney Mara, Joaquin Phoenix
Rooney Mara and Joaquin Phoenix. Todd Williamson/January Images/Shutterstock

"They were talking to one another nonstop," a source told PEOPLE at the time. "Small talk between them. Then they went for their car and he's holding her hand like it was unconscious. Like it fits. They seem a totally natural and easy couple."

The two got engaged last year, first sparking rumors in May when The Girl with the Dragon Tattoo actress was photographed wearing a large diamond ring on her left hand.

"She's the only girl I ever looked up on the internet," Phoenix told Vanity Fair of Mara in a November cover interview. "We were just friends, email friends."

Rooney Mara and Joaquin Phoenix
Rooney Mara and Joaquin Phoenix. VALERIE MACON/AFP via Getty

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Still, even as "just friends," Phoenix couldn't help but want to know more about the actress. "I'd never done that. Never looked up a girl online," he added.

Phoenix and Mara stepped out together earlier this year for the Golden Globe Awards and the Academy Awards, where Phoenix took home coveted top acting trophies at each ceremony for his performance in Joker.

After winning the TIFF Tribute Actor Award at the Toronto International Film Festival last September, he used his acceptance speech to honor his late brother River Phoenix and thank his fiancée for her support.

"One last thing — somewhere here, I don't know where, is a filthy dragon, and I want to rip its wings off and fasten a blanket and sleep with it forever," he said. "I love you. Thank you."

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