New York, New York - Robert Downey Jr. announced that his father, Hollywood legend Robert Sr., has passed away at age 86.

On Wednesday, the Iron Man star shared on his Instagram that his father died in his sleep on Tuesday night after a battle with Parkinson's disease.

"He was a true maverick filmmaker, and remained remarkably optimistic throughout," Robert wrote.

He added that he was thinking of his stepmother Rosemary, who wed his father in 1998, but joked "were happily married for just over 2000 years."

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Robert Sr. directed several films such as Greaser Palace and Up in the Academy, and starred as an actor in the cult classic Boogie Nights.

In addition to his famous son, the late legend was also father to Alyson from his first marriage to his frequent collaborator, Elsie.

Robert Jr. recalled during an interview in 2016 that his father was always treated with reverence amongst his peers.

The 56-year-old also credited his parents for his career in filmmaking and acting.

Previous to the passing of his father, Robert Downey Jr. has been recently raising eyebrows on social media for a different reason.

Fans noticed that he wasn't following his Marvel costars online, a departure from his past habits.

In fact, users pointed out that the actor is now only following 43 people, and his superhero pals, including Tom Holland and Chris Hemsworth, weren't on the list.

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Some speculated that the actor's mysterious move was a ploy alluding to his return to the Marvel Cinematic Universe.

But given the actor's devastating loss after his father's poor health, there could be other reasons for his decision – including moving on with his life and focusing on the next chapter.

Our thoughts are with the Iron Man star and his family.