The actor played Tony Stark, AKA Iron Man, in 10 films in the popular superhero franchise.
Though his character was given a hero’s send-off in 2019’s Avengers: Endgame, Marvel fans had speculated that Downey could return to the MCU in the future.
However, many fans were shocked to see Downey cull his list of Instagram follows, with some taking it as a sign that the actor was severing ties to the Marvel universe.
“In addition to dusting Thanos and his army out of existence, Robert DowneyJr. dusted his #Marvel co-stars on Instagram,” wrote one Twitter user.
“I wasn’t ready for RDJ to unfollow the whole Marvel cast, it’s like the end of an era,” wrote another.
“I don’t know what’s happening Mr Stark... WHYYY DID YOUU UNFOLLOW THE MARVEL CAST ON INSTAGRAM?” asked someone else.
The actor now only follows 43 accounts on the social media website, none of whom are actors.
Black Widow is the latest entry in the MCU, and is available to watch in UK cinemas now. The film will arrive on Disney Plus via paid Premiere Access on Friday, 9 July.