WARNING: Major spoilers ahead for Avengers: Endgame.
The Marvel movie has been enjoyed by audiences worldwide – earning record grosses.
But where it breaks from tradition with previous movies from the studio is that there is no credits scene of any kid.
There is, however, a brief audio stinger at the very end.
Theories have been running abound as to whether it’s the sound of Tony Stark (Robert Downey Jr) putting his suit together in 2008’s Iron Man, or even if it’s Harley Keener making his own suit.
It was even speculated to be a death toll by some viewers.
Now, the Russo brothers have clarified exactly what it is.
“There is indeed a sound of iron, which is to say goodbye to [Tony] in our way,” Joe told Chinese website ent.qq.com.
Indeed, much of the final part of Endgame is the farewell to Tony Stark.
Robert Downey Jr’s character dies in the final showdown against Thanos when he uses the Infinity Stones to perform his own Snap – wiping out all of the villains who were invading earth.
In a separate interview, the screenwriters have reflected on Tony’s exit – and said it was always the plan for him to bid farewell in this film.
“Everyone knew this was going to be the end of Tony Stark,” Steven McFeely told the New York Times.
Christopher Markus added: “I don’t think there were any mandates. If we had a good reason to not do it, certainly people would have entertained it.”
Asked if they entertained any other outcomes for him, Markus said: “No. Because we had the opportunity to give him the perfect retirement life, within the movie.
“That’s the life he’s been striving for. Are he and Pepper going to get together? Yes. They got married, they had a kid, it was great.
“It’s a good death. It doesn’t feel like a tragedy. It feels like a heroic, finished life.”
They also explained how they nearly had Hawkeye meet the fate that ultimately met Black Widow.
Avengers: Endgame is out now.