The new Avengers: Doomsday trailer has fans convinced there's a huge Doctor Doom twist hiding in plain sight, and Cillian Murphy is a key part of the theory

Avengers: Doomsday just dropped a "special look" at D23 over the weekend, and a major new theory has caught on like wildfire among fans, suggesting that Robert Downey Jr. might not be the movie's true Doctor Doom after all.

For two years now, we've known that Robert Downey Jr. is returning to the MCU, not as Tony Stark, but as Victor von Doom. However, in the latest "special look," a close-up of a masked Doom opening his eyes has people questioning whether RDJ is the movie's only Doom. RDJ, you see, has brown eyes, and the Doom under the mask seen in the trailer appears to have blue eyes, with no visible contact lenses. Curious...

And that's not all. Back at SDCC in July, we got a first proper look at Doom's costume and mask. The same costume that Doom appears in during the special look's closing moments, where Doom raises an army of Sentinels from the scrapheap after swatting Thor away like a mosquito.

But at D23 this past weekend, Marvel displayed a second, less ornate Doom costume and mask that more closely resemble the outfit Doom appears to be wearing in the Fantastic Four: First Steps post-credits scene, and during a brief moment in the Doomsday special look where Doom is ejected from a window and makes a superhero landing. Check out both costumes side-by-side below.

What does all this mean? There are a couple of potential explanations. The most likely is that, at some point in the movie, Doom undergoes something of a transformation. It seems likely that Doom will initially act the hero and potentially work with the Avengers, only to turn on them. The surprise in Reed Richards' voice when he asks Victor, "Did you do this?" in the special look would imply as much. Whether this ruse would be a sensible storytelling choice is another question; after all, we all know Doom is a wrong 'un.

The second, more out-there theory is that RDJ's Doom is a no-frills good guy who is at some point killed by an evil Doom variant. Due almost entirely to the blue-eyes theory, the internet has decided that said Evil Doom must be Cillian Murphy because… well, he has blue eyes. We'll admit, it's a stretch, not least because Marvel variants often have the same face in the MCU (though not always). But there are few actors on the planet with the stature to play a second Doom opposite RDJ, and Murphy is certainly one of them.

Whatever the truth may be, there's not long to wait to find out, as there's just over four months to go till Dunesday. Plenty of time to watch the list of "essential" pre-Doomsday movies and shows that Disney has just released, though we'd add a couple of omissions to that list.

Avengers: Doomsday releases in theaters on December 18. For more, check out our list of upcoming Marvel movies and shows, and get up to speed with the Marvel timeline with our handy breakdown.