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Serving as the culmination of The Infinity Saga and over 20 superhero films throughout the last decade, there were a lot of expectations riding on Avengers: Endgame. And while the film wasn't without a lot of laughs, it was also an emotional and somber experience set after Thanos defeated Earth's Mightiest Heroes and wiped out half of all life throughout the universe.

But while the Avengers had to regain their composure after such a stunning defeat, one of the most emotional scenes came down to a personal vendetta between two of the most prominent heroes in the Marvel Cinematic Universe. And given that it involved Robert Downey Jr.'s Iron Man, fans shouldn't be surprised to learn that the scene was mostly improvised while filming.

While speaking on the Empire Podcast, directors Joe and Anthony Russo broke down the film's biggest scenes — including the emotional confrontation between Iron Man and Captain America after all of their drama from Captain America: Civil War.

"I think that was one of Downey's most inspired performance moments in the movie," said Anthony during the podcast. "He very much reverts to, this is the guy who felt forsaken by his father – you can see his intimacy and trust issues in that moment when he turns on Cap. Downey performed the scene with a lot of energy. We didn't do it many times, because he was expending himself so, so much. He understood it very well.”

The directors have long praised Downey's presence on the productions, rising up to the challenge to complete his character's story that began in the first Marvel Studios film Iron Man over a decade ago.

Because of his skill as well as his intimacy with the character, they allowed Downey a little but of leeway when it came to filming his biggest scenes, including the one where he fatefully snapped his fingers with the Infinity Stones, defeating Thanos while also sacrificing himself in the process.

Apparently those scenes were so intense that Downey almost dropped the first F-bomb in the MCU, according to Avengers: Endgame writers Christopher Markus and Stephen McFeely.

"I think at one point he said f*** you at one point (laughs). Didn't he say f*** off?" McFeely asked on the podcast.

"He may have said...you do a lot of takes," Markus said.

"It was like can we really end all this on a complete swear," McFeely said, with Markus adding

"Or a kiss my ass Thanos".

"And that one just seemed to bring it all back around to the beginning, and to be why he did it, because he's a hero, finally," Markus said.

Instead, Iron Man brings everything full circle when saying "I am Iron Man," and restores the balance of the universe in the process.

Avengers: Endgame is now playing in theaters.