Robert Downey Jr has announced he will return to the Marvel film franchise as the villain Doctor Doom.

The 59-year-old surprised fans at Comic-Con in San Diego on Saturday night when he was dramatically unmasked by a Marvel panel.

Addressing crowds after the announcement that he will play a different character, he declared: "New mask, same task."

Downey Jr first appeared as Iron Man in 2008 - reprising the role in a further eight Marvel Comic Universe (MCU) films.

Avengers Endgame and Infinity War directors Joe and Anthony Russo confirmed they will direct Downey Jr's next MCU appearance in Avengers: Doomsday.

"When we directed Avengers: Endgame, Joe and I truly believed that it was the end of the road for us in the Marvel Cinematic Universe," Russo said on Saturday.

"In the time since, through a very special story, Joe and I have come to potentially see a road forward with you."

Downey Jr's most recent cinematic success was at the Oscars, winning best supporting actor for his role alongside Cillian Murphy in Oppenheimer.