Robin: I didn't have mercy on film
Robin Williams' latest role is in a film made by one of his friends - but he's insisted he didn't take the part "as a mercy thing".
The actor plays the lead in the blisteringly dark film, and but he was originally only going to play a cameo.
Writer and director Bobcat Goldthwait said: "Actually Robin read the script for World's Greatest Dad and was going to help me out and play a small part.
"Then he called and said, 'Can I play the lead?' I was like, 'Woah!' I mean Robin's one of the finest actors in the world, so to have him want to be [the lead] in my movie changed everything."
Robin added: "I didn't do this as a mercy thing, like, 'Oh, I'll help little Bob'.
"I really thought it was well written and I also know him as this really savvy film guy."
Sky Kids actor Daryl Sabara plays Robin's character's tortured and unruly son.
Robin said of him: "He's amazing, he's fearless. In real life Daryl is a sweet kid but plays Karl as a little p***k and unrelentingly so!"
:: World's Greatest Dad is released in selected cinemas on Friday, September 24.