EXCLUSIVE: Joaquin Phoenix and fiancée Rooney Mara look every inch the doting new parents with baby boy River during stroll in Santa Monica

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Joaquin Phoenix and his fiancée Rooney Mara looked every inch the doting first-time parents as they returned to their Santa Monica home on Friday. 

After running errands as a family-of-three, the 46-year-old Oscar winner could be seen cradling his precious baby boy River. 

Keeping a low profile, the Joker star wore a black t-shirt, matching beanie, sweatpants and a face mask amid the ongoing COVID-19 pandemic. 

Proud dad: Joaquin Phoenix and his fiancé Rooney Mara looked every inch the doting first-time parents as they returned to their Santa Monica home on Friday

The back of his sweatshirt read: 'Save animals, bear witness, go vegan.' 

Mara, 35, who gave birth to their son in September, rocked a striped shirt, beige cardigan an Converse sneakers.   

Earlier in the day, she was responsible for holding their infant, who was dressed in a green and purple tie-dye shirt and striped pants. 

Quality time: After running errands as a family-of-three, the 46-year-old Oscar winner could be seen cradling his precious baby boy River

As they walked across the street, Phoenix stayed close to Mara's side as she toted a large bag and kept her brown tresses in a low bun. 

They both wore sunglasses to block out the California rays as they enjoyed the warm weather. 

Phoenix wore a pair of white headphones around his neck and looked relaxed with one hand in his pocket.  

Family-of-three: Keeping a low profile, the Joker star wore a black t-shirt, matching beanie, sweatpants and a face mask amid the ongoing COVID-19 pandemic

The couple welcomed their son last fall, naming him after Joaquin's late brother River Phoenix, who died at 23 years old in 1993. 

Director Victor Kossakovsky spilled the beans at the 2020 Zurich Film Festival in September, after a screening of the film Gunda, on which Joaquin served as executive producer.  

He slipped in the news during a Q&A, after he was asked how he got the new dad involved in the film: 'He just got a baby by the way... A beautiful son called River.' 

First-time mom: Mara, 35, who gave birth to their son in September, rocked a striped shirt, beige cardigan an Converse sneakers

Paying tribute: The couple welcomed their son last fall, naming him after Joaquin's late brother River Phoenix, who died at 23 years old in 1993

Sunny day: Earlier in the day, she was responsible for holding their infant, who was dressed in a green and purple tie-dye shirt and striped pants

River died at the peak of his career, with memorable roles in Stand By Me (1986), Indiana Jones and the Last Crusade (1989), and Gus Van Sant's My Own Private Idaho (1991) already under his belt. 

In September, Joaquin opened up about his late brother's legacy in a rare interview with Anderson Cooper for 60 Minutes.

The actor said: 'I feel like in virtually every movie that I made, there was a connection to River in some way. And I think that we've all felt his presence and guidance in our lives in numerous ways.'     

Growing family: The animal rights advocates live in the Hollywood Hills with their two dogs Soda and Oskar, and their engagement was confirmed in July of 2019, a few months after she was first spotted wearing her engagement ring (pictured in November, 2013)

Gone too soon: River died at the peak of his career, with memorable roles in Stand By Me (1986), Indiana Jones and the Last Crusade (1989), and Gus Van Sant's My Own Private Idaho (1991) already under his belt

They subtly confirmed the news of their firstborn's arrival in November, when they mentioned him in an op-ed for People about the migrant children crisis. 

Rooney began dating her Her (2013) costar in late 2016, and they later starred together in Don't Worry, He Won't Get Far on Foot and Mary Magdalene, both of which premiered in 2018. 

The animal rights advocates live in the Hollywood Hills with their two dogs Soda and Oskar, and their engagement was confirmed in July of 2019, a few months after she was first spotted wearing her engagement ring. 

Beloved brother: Joaquin opened up about River's legacy in September: 'I feel like in virtually every movie that I made, there was a connection to River in some way. And I think that we've all felt his presence and guidance in our lives in numerous ways' (pictured in 1985)

Onscreen romance: Rooney began dating her Her (2013) costar in late 2016, and they later starred together in Don't Worry, He Won't Get Far on Foot and Mary Magdalene, both of which premiered in 2018