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 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.'"
