The group were guaranteed £2 million each for fulfilling the terms of their record contract but it was only valid if all five members were still part of the band, and the 22-year-old singer felt he had already made as much money as he needed so didn't have an ''incentive'' to stay.
A source said: ''There's a massive loyalty bonus for each member if they fulfil their record deal.
''But Zayn didn't even want the money. All he ever wanted was to buy his mum a house - and he's done that so there was no incentive for him to finish the tour let alone make a fifth album only to spend another six months on the road.''
A friend told heat magazine: ''He texted the boys then announced it [publicly]. I don't think he wanted anyone to be able to talk him out of it.''
Though Zayn said he was leaving to lead a ''normal'' life, he has been recording solo material with producer Naughty Boy, who posted a demo of the pair's first collaboration online earlier today (31.03.15).
A source said: ''Apparently [the songs] are 'very Ne-Yo'.
''He's also been speaking to Pharrell to get feedback on his demos.''
'No Turning Back' was released on this day (January 3rd) in 2003.
Bastille rocked up at The Winter Gardens in Margate for their 'Doom Days Club Nights' tour, making sure they were playing in more unfamiliar towns...
Stealing Sheep made their way down to Elsewhere in Margate to put on their wholly unique and utterly captivating live show.
Listen to her new single 'Down'.