Downey Jr., who played Iron Man in ​earlier “Avengers” blockbusters, will appear in “Avengers: Doomsday” as the villain Doctor Doom. The ​movie is the first from Walt Disney-owned Marvel to unite the ⁠Avengers and the X-Men.

“Honestly, I could not have imagined reuniting with this amazing ​team, after such a glorious run of success and creative joy, let alone ​as a new character,” Downey Jr. said on stage at the CinemaCon convention of theater owners.

Evans, who portrayed Steve Rogers and his alter-ego Captain America in earlier Marvel films, said his ​return was unexpected.

“I said I would only come back if there was a ​real reason, and in ‘Doomsday,’ there is a very real reason that these heroes need Steve Rogers ‌now,” ⁠he said.

In scenes shown to the CinemaCon crowd, Thor, played by Chris Hemsworth, is heard saying “we are going to need a miracle,” before spotting Rogers.

The CinemaCon crowd responded with rousing applause and cheers, prompting Downey Jr. to ask for the ​trailer to be played ​a second time.

Marvel ⁠movies have generated nearly $33 billion at global box offices, the highest total for any film franchise.

“Avengers: Endgame,” released in 2019, ​is the second-highest-grossing movie of all time.

“Avengers: Doomsday” will be ​released on ⁠December 18, the same day as the third instalment of Warner Bros’ sci-fi series “Dune”, setting up a box office battle dubbed “Dunesday.”

Cinema operators said they believed both movies to ⁠be ​among the year’s biggest releases.

Disney also promoted the ​upcoming “Star Wars” film “The Mandalorian and Grogu,” which heads to theaters in May, and a live-action version of “Moana” ​that is due for release in July.