Joaquin Phoenix and Rooney Mara welcome baby boy named 'River'

Joaquin Phoenix and Rooney Mara have welcomed a baby boy named River. Photo / Getty Images

Joaquin Phoenix has reportedly welcomed his first child, a baby boy, with his fiancee Rooney Mara.

The pair named their child River Phoenix in honour of Joaquin's late brother of the same name, who died in 1993.

Russian director Viktor Kossakovsky announced the news at the 2020 Zurich Film Festival, where he was screening his new film Gunda, which Joaquin was an executive producer on.

When asked how he managed to lure Joaquin to produce Gunda, Kossakovsky said: "He just got a baby by the way … A beautiful son called River."

It is understood Rooney gave birth a month ago, however there is no official word from Joaquin or Rooney on the birth yet.

River, who shot to notoriety in the 1986 film Stand By Me and fast became one of the most popular actors in Hollywood, died of a drug overdose at the age of 23 in West Hollywood.

US actor, musician and activist River Phoenix died in 1993. Photo / Getty Images

He was with his actress girlfriend Samantha Mathis, Johnny Depp, members of the Red Hot Chili Peppers, Christina Applegate and siblings Joaquin and Rain at Depp's Viper Room club on the night of his death.

Joaquin made a frantic call to emergency services where he was heard saying, "Please come, he's dying, please."

Joaquin Phoenix won the Oscar for best actor this year. Photo / Supplied

The actor was pronounced dead at Cedars-Sinai Hospital after an overdose of cocaine and heroin.

During his acceptance speech for Best Actor at the Academy Awards this year for Joker, Joaquin honoured River by saying: "When he was 17, my brother wrote this lyric. He said: 'Run to the rescue with love and peace will follow.'"

Joaquin and Rooney began dating in 2016 after meeting on set of the film Mary Magdalene, and became engaged last year.