As the filmmaker’s three-year journey wound down on the project, he realized a key moment was missing, and managed to shoot it within a few months of the film's opening.

The upcoming film stars Pedro Pascal as Reed Richards/Mr. Fantastic, Vanessa Kirby as Sue Storm/Invisible Woman, Ebon Moss-Bachrach as Ben Grimm/The Thing and Joseph Quinn as Johnny Storm/Human Torch.

When Entertainment Weekly asked Fantastic Four: First Steps director Matt Shakman if Downey Jr. filmed that post-credits scene, the filmmaker pleaded the fifth. "For others to talk about," he teased. However, Shakman did reveal that it was the Russo brothers who helmed the post-credits scene since it was shot for Avengers: Doomsday.

First Steps director Matt Shakman was discreet when questioned about Robert Downey Jr.’s role in the post-credits scene, choosing not to reveal any details and leaving the discussion to fans.