Robin Williams and director Bobcat Goldthwait have revealed some of the on-set antics when filming World's Greatest Dad.

The pair, who are busy promoting the movie, admit they loved working together.

Williams says Bobcat has one odd directing trait: "The only thing that is slightly strange is that he will wear hats that are so bizarre, just so you can't take him seriously when he gets mad."

Goldthwait added: "It is actually to prevent myself from getting mad. If you scream at someone when you are wearing a sombrero then you are a douchbag."

Worlds Greatest Dad is released in cinemas across the UK on Friday 24 September.