Avengers: Endgame is full of dozens of showstopping sequences, the kind of moments that make audiences clap, cheer and even shed tears. But there’s one moment in particular that is not only Robert Downey Jr.‘s finest moment in Avengers: Endgame, but one the most pivotal scenes in the entirety of his appearances in the Marvel Cinematic Universe. Funnily enough, it’s a moment that wasn’t written in the script, and it was a last minute addition thought up in the editing room before the production’s planned reshoots.

Find out all about how it came to be below, but beware of major spoilers.

/Film reader Will C. was lucky enough to be in attendance at an event in Washington DC with filmmakers Anthony & Joe Russo, and he sent over the audio from this nearly hour-long Q&A session with the filmmakers behind Avengers: Endgame. During the event, Anthony & Joe Russo talked about the challenges of shooting the epic final battle between all of The Avengers and hundreds of other warrior allies and Thanos and his entire arsenal of aliens, creatures and weapons.

During this conversation, one of the Russo brothers revealed a shocking detail about Tony Stark’s death scene, where he delivers one final line before using the Infinity Stones to wipe out Thanos and his entire army. In that scene, Thanos believes he’s won by again possessing all the Infinity Stones and says, “I am inevitable.” But when he snaps his fingers, nothing happens. That’s because Tony’s nanotech Iron Man armor took hold of the stones and situated them into a makeshift gauntlet formation. Before snapping his fingers to stop this battle once and for all, he says, “And I am Iron Man.”

It’s a moment that brings the Marvel Cinematic Universe and Tony Stark’s character arc full circle after beginning this long line of films back in 2008. But it wasn’t in the original script. In fact, the moment didn’t even come about until Anthony & Joe Russo were working on the final battle in the editing room. The directors explained:

“Tony used to not say anything in that moment. And we were in the editing room going, ‘He has to say something. This is a character who has lived and died by quips.’ And we just couldn’t, we tried a million different last lines. Thanos was saying “I am inevitable.” And our editor Jeff Ford, who’s been with us all four movies and is an amazing storyteller, said ‘Why don’t we just go full circle with it and say I am Iron Man.’ And we’re like, ‘Get the cameras! We have to shoot this tomorrow.'”

Props to Jeff Ford for coming up with the moment that truly seals the deal in this epic battle. Iron Man’s sacrifice doesn’t feel nearly as powerful without that callback line. It means so much to Tony Stark as a character that there’s no better way for him to go out than that. It’s just incredible that this line didn’t even make it in front of cameras until January, mere months before the movie was slated to hit theaters.

There was one other fun fact that Anthony & Joe Russo revealed about this final moment. In addition to being the final scene they directed for Marvel Studios (for now), as well as the final shot delivered by the visual effects department, the location where these reshoots took place was at Raleigh Studios in Hollywood, California. Catty-corner to the stage they were shooting on was the place where Robert Downey Jr. had screen-tested 12 years previously for the first Iron Man. And that’s what you call a full circle.