Fantastic Four: First Steps is hiding a musical Easter egg from Avengers: Doomsday

The Fantastic Four: First Steps might be a standalone Marvel movie, but it does make sure to set up Avengers: Doomsday.

The following will contain spoilers for The Fantastic Four: First Steps, so turn back now if you're not up to date!

Now, if you're still reading, then you'll know that Doctor Doom shows up in the Fantastic Four post-credits scene. This is presumably Robert Downey Jr.'s version of the character, though we don't see his face, since it's hidden by a green cloak.

He's sitting with Franklin, though what he might want with the child is unclear. We're willing to bet it has something to do with the Power Cosmic, but what Doom intends to do with that power is a mystery for now.

During this scene, though, Avengers composer Alan Silvestri's "Doom?" theme can be heard in the background, as revealed by the credits. That seems to be confirmation that this is indeed RDJ's Doom, thanks to that Avengers link.

Whether Doom is from Earth-828 or if he arrived from another universe remains to be seen, though we're wondering if his arrival is what spurs Marvel's First Family to venture to the main Marvel universe in search of help, as seen in the Thunderbolts* post-credits. Whatever is going on, we're sure to find out soon when Avengers: Doomsday arrives next December.

The Fantastic Four: First Steps is in UK cinemas now and US theaters from July 25. In the meantime, check out our guides to watching the Marvel movies in order and all the upcoming Marvel movies and shows.