Simon Cowell is ''really sad'' Zayn Malik has quit One Direction, according to his ex-girlfriend Sinitta.

The 51-year-old star - who has also previously dated Brad Pitt - has revealed the music mogul is ''really proud'' of Zayn despite his decision to quit the group after taking time off from their current tour due to stress.

Sinitta shared: ''Simon just said that that he's really proud.

''He's really proud and I think he's always known that this was always a reluctant thing for Zayn to do, so the fact he's managed to stay this long and done so well, I think he's really proud of him but obviously we're really sad as well.''

Although Zayn's announcement came as a shock to Sinitta, she claims she's always known there were troubles in the group - which also includes Harry Styles, Louis Tomlinson, Liam Payne and Niall Horan - and insisted it was hard work convincing the 22-year-old star to join back when they were contestants on 'The X Factor'.

Speaking on ITV's 'This Morning', she explained: ''I didn't know that he was going to be leaving, I knew that there were troubles but the funny thing is, Zayn, he was always the most reluctant.

''Even in the early days when we wanted them to dance and there was choreography ... he was always the shy one at the back.

''He has an incredible voice, beautiful boy, really sweet but just very, very shy and introverted so it was hard to get him to even be in the band in the first place.''

Zayn's decision to quit the most successful boyband in the world came after pictures of him and a girl named Lauren Richardson holding hands at a nightclub in Thailand emerged, threatening his relationship with his Little Mix star fiancee Perrie Edwards.