Zayn Malik quit One Direction because he was sick of their endless touring, according to the boy band's songwriter Jamie Scott.
The singer stunned fans in March (15) when he announced he was walking away from the group in a bid to lead a "normal" life, and Scott, who helped write songs including Story of My Life, is convinced Malik was fed up of the band's non-stop touring schedule.
Scott tells Britain's Sunday People newspaper, "Zayn went because he'd had enough. Have you ever been on the road for four years? These guys aren't at home... There is no way the same thing is going to run through all five guys, that they're all going to want to be on the road so much together. Eventually he got to a point where he'd had enough.
"It was, 'OK, I don't want to be in this band any more'. It was that simple, it was human instinct kicking in. People want it to be complicated and have secret reasons but that is what it was."
Malik has been working on solo material in the recording studio since his departure.