For now, Marvel is believed to only be shooting scenes for Doomsday, with the timing of Reynolds' post strongly suggesting he's set to return for that, rather than later down the line. Indeed, some fans are eagerly anticipating a second big reveal of Avengers: Doomsday cast members, perhaps via a second set of chairs, as production continues.

A cryptic new Instagram post from Ryan Reynolds has fans speculating that the actor could be returning as Deadpool in "Avengers: Doomsday."

Doomsday? A cryptic post has fans buzzing, but his addition could create problems for Marvel. Find out what challenges a PG-13-rated Avengers movie could face with Deadpool in the mix.