WARNING: The following article contains major spoilers for Avengers: Endgame, in theaters now.

As the culmination of 21 films released over the past 11 years, Avengers: Endgame marks the end of an era for the Marvel Cinematic Universe. For directors Joe and Anthony Russo, it also represents the end of a working relationship with Marvel Studios that began with 2014's Captain America: The Winter Soldier. The filmmakers appeared at spotlight event held Tuesday by the Smithsonian Institute in Washington, D.C. to discuss Endgame and their earlier work for Marvel.

The directors were asked about re-staging the celebrated elevator sequence from The Winter Soldier, the first scene they ever filmed for Marvel. Joe Russo noted it was much easier and faster to recreate the scene as Captain America boards an elevator full of undercover Hydra operatives, faithfully positioned in the same manner as they had been in the 2014 film, with many of the original stunt team returning for the sequence.

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Standing in contrast, their final scene for the MCU was a nod to the closing of 2008's Iron Man, the film the launched the blockbuster franchise. Shot in January in Los Angeles, during additional photography for Endgame, it's the moment when Robert Downey Jr.'s Tony Stark declares "I am Iron Man" before using his Gauntlet to disintegrate Thanos and his entire army, but at the cost of his own life.

The Russos had filmed the scene earlier, only without Tony saying anything before he snapped his fingers. As the movie entered post-production, however, the filmmakers felt it lacked emotional impact. The normally hyper-verbal Tony would have one final comment before making his sacrifice, they reasoned. As they reviewed a rough cut, veteran film editor Jeffrey Ford suggested a callback to the iconic moment from Iron Man.

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While the majority of the film was shot in Atlanta, the final round of reshoots was completed in Raleigh Studios in Los Angeles. Anthony Russo observed that, in a completely unintentional moment of symmetry, the studios are located across the street from the offices in which Downey filmed his screen tests for Tony Stark.

Joe Russo joked that the way everything unfolded made it appear as if it was planned all along, instead of at the literal last minute of filming.

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Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr. as Iron Man, Chris Evans as Captain America, Mark Ruffalo as Bruce Banner, Chris Hemsworth as Thor, Scarlett Johansson as Black Widow, Jeremy Renner as Hawkeye, Brie Larson as Captain Marvel, Paul Rudd as Ant-Man, Don Cheadle as War Machine, Karen Gillan as Nebula, Danai Gurira as Okoye and Bradley Cooper as Rocket, with Gwyneth Paltrow Pepper Potts, Jon Favreau as Happy Hogan, Benedict Wong as Wong, Tessa Thompson as Valkyrie and Josh Brolin as Thanos.