Doomsday is now playing in theaters ahead of Avatar: Fire and Ash, and the brief glimpse into the upcoming Avengers film has already revealed several notable details. From surprising character appearances to potential clues about the future of the MCU,

Marvel made the somewhat baffling decision to produce theatrical-only teaser trailers for Avengers: Doomsday, a full year ahead of release. Now, of course, they have leaked online. Spoilers follow, although no one can be blamed for that but Marvel.

The sudden appearance of a cryptic symbol has added credence to one compelling theory about "Avengers: Doomsday."