The ending of "Avengers: Endgame" had made not just the audience sad but also left its lead man, Robert Downey Jr., heartbroken, reveals director Joe Russo.

The co-director of Marvel's highest-grossing movie has revealed in the new book, "The Story of Marvel Studios: The Making of the Marvel Cinematic Universe," that Downey Jr. cried when he told him about the fate of Tony Stark, aka Iron Man, in the movie.

"When the Russos' presentation to Downey Jr. got to Tony Stark's last moments, their nerves began to fade," the Marvel book mentioned. "But their belief in the story was solidified."

Joe, who directed the movie with his brother Anthony, recalled the moment he narrated the story to the actor and got to the beloved superhero's death.

"Robert started crying and when we were done, he said 'That's f--king awesome.' That's when we knew that we had to do it. Because he felt it," the co-director said.

The action-packed sci-fi movie was released on April 26, 2019. While Downey Jr. was emotional regarding the ending, he was not shocked about Iron Man's destiny.

The 56-year-old actor already had an idea about his character's arc before he signed, "Captain America: Civil War," which was also directed by the Russo brothers. Downey Jr., who played the title character in the 2008 movie "Iron Man," helped shape the Marvel Cinematic Universe.

The new book features stories about the cast and crew members of Marvel movies.

In the book, Downey Jr. thanked actor Terrence Howard for his casting as Iron Man.

"While I have your car, I'll reach way back to day one, and express gratitude to Howard (our original Rhode), who was integral to my being cast," the actor wrote.

Downey Jr. is now working in a comedy sports drama, "All-Star Weekend," which is under post-production. He will also appear in the miniseries "The Sympathizer," which is under pre-production.

Two movies under Marvel Cinematic Universe's Phase Four – "Black Widow" and "Shang-Chi and the Legend of the Ten Rings" – have already been released this year. Fans will be treated with two more movies, "Eternals" and "Spider-Man: No Way Home," soon.

"Eternals" is scheduled to release on Nov. 5, while "Spider-Man: No Way Home" will drop on Dec. 17.

Robert Downey Jr.
Robert Downey Jr. teased that he was preparing for "Sherlock Holmes 3." He is pictured at the "Avengers: Infinity War" premiere on April 23, 2018 in Los Angeles. Emma McIntyre/Getty Images
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