LOS ANGELES -- Actor Robert Downey Jr. is joining the directors of "Avengers: Infinity War" in calling for fans to maintain secrecy.

He signed it with the (hashtag) ThanosDemandsYour Silence. Thanos is the fictional Marvel Comics villain who will be portrayed by Josh Brolin in the movie. Downey plays Iron Man.

Directors Joe and Anthony Russo went on Twitter to tell fans they would be screening a limited amount of footage prior to the film's release on April 27. They say "only a handful of people know the film's true plot."

They asked fans to maintain the same level of secrecy so that they don't spoil it for others.