Zayn Malik has ADHD.

Zayn Malik

Zayn Malik

The 'Pillowtalk' hitmaker was "pretty wild" and struggled to concentrate when he was younger, and it was only years later he was diagnosed with Attention Deficit Hyperactivity Disorder.

He revealed in his new memoir 'Zayn': "[Growing up] I was pretty wild. I could never focus, couldn't get a handle on where my brain wanted to go. I was constantly getting in trouble.

"Once, when I was at Tong High School, I was collared for a BB gun in class. It wasn't loaded or anything, but me waving it around didn't go down too well. I was later diagnosed by doctors as having super-hyperactivity--or ADHD (Attention Deficit Hyperactivity Disorder) as they like to label it."

The 23-year-old singer - who also revealed in his book he suffered from an eating disorder - has cancelled a number of solo performances since leaving One Direction because of his struggles with anxiety and he admits he found his problems "more manageable" when he was in the band.

He wrote: "Anxiety is nothing to be ashamed of; its affects millions of people every day. I know I have fans out there who been through this kind of thing and I wanted to be honest for their sake.

"When I was in One Direction my anxiety issues were huge, but within the safety net of the band, they were at least manageable.

"As a solo performer, I felt much more exposed and the psychological stress of performing got too much. Rather than hiding away, sugar- coating it, I knew I had to put it all out there."

Despite his successful recording career, Zayn - who is dating Gigi Hadid - is keen to return to education in the future.

He admitted "Maybe I could do a course from home - either in London or LA - and I reckon graduating would feel just as big a personal achievement as releasing an album or performing on tour."