Writer and director Joss Whedon
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Avengers director Joss Whedon: 'There was doubt'

After two years in the making, Avengers sequel Age of Ultron was released in the UK on 23 April and is out in the US on 1 May.

The BBC's Lizo Mzimba went behind the scenes to meet the writer and director of the film Joss Whedon.

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