It's no joke: Joaquin Phoenix and Will Sage AstorRooney Mara's family is getting bigger.

The Joker star and the Girl With the Dragon Tattoo actress are expecting their second baby three years after welcoming son River, multiple outlets reported Feb. 18.

Rooney debuted her pregnancy at the premiere of La Cocina at the Berlinale International Film Festival in Berlin Feb. 16. Clad in a strapless black ballgown, the 38-year-old cradled her growing baby bump as she walked down the red carpet.

E! News has reached out to reps for Rooney and Joaquin for comment and has not heard back.

Since they were first romantically linked in 2017—four years after costarring in Her—Rooney and Joaquin have been tight lipped about details about their relationship. However, in 2019, Joaquin offered rare insight into their love story.

"She's the only girl I ever looked up on the internet," the 49-year-old admitted in an interview with Vanity Fair, explaining how he initially thought Rooney hated him until he learned that she was just too shy to ask him out. "We were just friends, email friends. I'd never done that. Never looked up a girl online."

That same year, Rooney sparked engagement rumors when she was photographed wearing a diamond ring. However, neither publicly addressed the bling at the time.

In fact, the notoriously private couple largely kept details of Rooney's pregnancy with River—who was named after Joaquin's late brother River Phoenix—under wraps. Instead, news of his birth was shared by Joaquin's Gunda collaborator, director Victor Kossakovsky, who let slip in September 2020 that the Oscar winner had become a dad.

"Good baby by the way," the filmmaker shared at the Zurich Film Festival, adding that the pair have "a beautiful son."

While Joaquin and Rooney have continued to keep their baby boy away from the spotlight, their world perspective has altered since becoming parents.

As Rooney shares in a May 2021 letter, "Raising our baby, River, has opened my heart to a whole new life filled with hope and more determination than ever to create a kinder and more sustainable world."

"I feel so fortunate to be able to nurture my son in all of the ways that nature intended," she added, "and I wish all mothers in the animal kingdom could experience that sacred maternal bond with their young."

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