Joss Whedon, Avengers movie creator and director, has revealed two Marvel characters who will be joining the film’s sequel. Warning: Spolier Alert!

The director had previously teased the appearance of a "brother-sister act" in the upcoming sequel, but has now confirmed that Quicksilver and the Scarlet Witch will appear.

Talking to IGN, he said: "You know, they had a rough beginning. They're interesting to me because they sort of represent the part of the world that wouldn't necessarily agree with The Avengers.

"So they're not there to make things easier. I'm not putting any characters in the movie that will make things easier."

Whedon previously described the then-unnamed duo as "two of my favourite characters from the comic book."

It was reported last week that Saoirse Ronan is a contender for the role of the Scarlet Witch.

When asked if the plot of Iron Man 3 made it difficult to for Iron Man to appear in Avengers 2, he said: "Well, I feel like in Iron Man 3, even though he said, 'I’ve changed' - he blew up his remote suits, but I don’t think anybody thinks he doesn’t have one anymore.

"The question is, if The Avengers are called, does he show up? And the answer is, ‘Yes!’"