Spurlock reveals the 22 year old was clearly struggling with fame, attention and his place in the band.

The Super Size Me director says, "He always struggled with being on the road. He's a homebody. He wanted nothing more than to sit in his house and spray paint and draw and do art, and I think this explosion that happened to him - which was something none of them ever predicted... I think he was the one who struggled with it the most.

"And being away (from home), being on the road, being away from his girlfriend I think finally just got to him, and I think he said, 'I'm done'."

Malik announced he had left the group last week (ends27Mar15) as One Direction wrapped up a tour of Asia.