Robert Downey Jr. mourns death of father Robert Downey Sr. at 85

Marvel star Robert Downey Jr. has paid tribute to his father, Robert Downey Sr., who died on Tuesday at age 85, after battling Parkinson's disease.

Taking to social media to share the sad news, the 56-year-old Hollywood actor shared a black and white photo of his father, who was also an actor, director, producer and writer.

"RIP Bob D. Sr. 1936-2021. Last night, dad passed peacefully in his sleep after years of enduring the ravages of Parkinson’s [disease]," the Iron Man star wrote.

Downey Jr. called his father "a true maverick filmmaker," as he directed the 1969 countercultural satire Putney Swope — and other films that gained a cult following. But he noted that his dad "remained remarkably optimistic throughout" his battle with the nervous system disorder that affects movement.

"According to my stepmom's calculations, they were happily married for just over 2000 years. Rosemary Rogers-Downey, you are a saint, and our thoughts and prayers are with you," the 56-year old continued.

Robert Downey Jr. was from his father's first marriage to actress Elsie Ann Ford — and the Marvel star has a sister, Allyson Downey.

Father and son had a complicated relationship with Robert saying they used drugs together as a way to bond when he was a child.

"It was like [my dad] trying to express his love for me in the only way he knew how," he said in 1988. The Sherlock Holmes star's struggles were very public in that area, though he put that behind him.

So did Downey Sr., telling Us Weekly back in 1996, "I wasn't around as much as most fathers. I was out making films. If Robert wanted to be wild, it was OK with me... I don't want to become like an A.A. babbling jerk, but if I knew then what I know now..."

Later in life, the men found healthier ways to bond — through family. Rob Jr., a father of three, has shared photos of his father with his own children.

Downey Sr.'s filmmaking career started in the '60s with his indie projects but he also worked on big-budget films like Greaser’s Palace (1972) and Up the Academy (1980). He also appeared in Boogie Nights (1997), Magnolia (1999) and Tower Heist (2011).

Father and son also appeared in several of the same films — like 1988's Johnny Be Good and many helmed by the senior Downey.

It's been a difficult period of loss for Downey Jr., whose longtime assistant and friend Jimmy Rich died in a car accident in May.

Additional reporting by Suzy Byrne.

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