Joss Whedon says that ever Avengers movies is going to have a new villain, and that is why Loki will not be returning in Avengers: Age of Ultron.
It was revealed earlier this year that Hiddleston would not be reprising the role of Loki for this film, however we will be seeing him later this year in Thor: The Dark World.
Speaking to Entertainment Weekly the director said: "Every movie is going to be a different villain. Loki's awesome, and he is awesome in Thor 2. But The Avengers is a different thing.
"I worked with Tom more than any other actor [on The Avengers], because he was the only villain and there were six heroes. And he was as great as anyone I've ever worked with, and I get why people loved the character. But it's an Avengers movie."
Whedon revealed at Comic Con that Ultron would be the villain second time around, but it is not yet known who will play that character.
Filming is set to get underway on Avenger: Age of Ultron at the beginning of next year for a summer 2015 release.
Robert Downey Jr, Chris Evans, Chris Hemsworth, Scarlet Johansson, Jeremy Renner and Mark Ruffalo are all set to reprise their roles.
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