Joss Whedon admits there's a ''thin wall'' between friendship and ''chaos'' for The Avengers.

The 50-year-old film-maker, who directed the eagerly-awaited 'The Avengers: Age of Ultron', has hinted the new movie will see plenty of ups and downs between the various superhero characters.

He told Marvel: ''There are two things you really want to see, I think, in the second Avengers. You want to see them getting along, and you want to see them not getting along.

''What we find is they can get along great, they're a team, but it's a thin wall between that and chaos. They do get kind of torn apart a little bit.''

Meanwhile, Elizabeth Olsen and Aaron Taylor-Johnson have been cast in the roles of Scarlet Witch and Quicksilver respectively, and Whedon has revealed their additions will prove crucial to the movie.

He explained: ''I wanted to be able to shoot something that was kind of poetic and strange - and her magic and his speed and the way they are and the way they hate The Avengers - it just adds so much to the palette. The two of them are just ridiculously great too.''