In a video interview with the U.K.-based outlet The Upcoming, Downey was asked what he thought of the still super-secret film.
"The last eight minutes of that movie were maybe the best eight minutes in the entire history of the whole run of them in a way...because everyone's involved. So I was delighted," he said.
It's rumored that this is the last film in which Downey Jr. and other cast members will appear. The entire Marvel Cinematic Universe kicked off with Downey's turn in 2008's "Iron Man."
It was now-Marvel Studios head Kevin Feige who dreamed of a connected MCU and directors Joe and Anthony Russo helped shape it. They directed "Captain America: The Winter Soldier," as well as "Captain America: Civil War," "Avengers: Infinity War" and "Endgame."
"Anthony and Joe are about the only two folks that I could imagine [directing the movie]," Downey said. "Forget just still having the respect of the cast and crew when we were done -- but not being either incarcerated or embalmed or in some other way permanently damaged, because just the physical and mental stripping of one's chi that it takes."
He added, "You know these are years, and years, and years, and years. They've essentially been on a job for six, seven years now. And I love them. And they love 'The Avengers.'"
"Avengers: Endgame" premieres April 26 from Marvel Studios, which, like ABC News, is owned by Disney.