The British singer shocked fans last year (15) when he walked away from the boy band, and he has since launched himself as a solo star.
Zayn embraced more of an R&B sound for his new material, and he promptly distanced himself from his clean-cut One Direction work by debuting the steamy Pillowtalk as his first single earlier this year (16).
The track, which featured a sexy video starring Zayn and his model girlfriend Gigi Hadid, was all about making love, and in his new autobiography, the 23-year-old admits he didn't hold back because he had been waiting a long time to embrace more mature subject matter in his music.
"Every lyric I've ever written has a story behind it," he explains in an excerpt from his forthcoming memoir, obtained by DailyMail.co.uk. "All the hard work that went into the creation of Pillowtalk was worthwhile because, as soon as it was finished, I intuitively felt I was on the right path."
"It was a sick cut, nailing the exact sound I wanted to capture in my music," he continues. "I was also able to sing about a subject that I hadn't really been able to go near while I was in One Direction: sex."
Pillowtalk featured on Zayn's album, Mind of Mine, and he scored a TransAtlantic chart double with both his debut solo single and album as the projects each hit number one in the U.K. and U.S. upon their release earlier this year (16).
The singer's book, simply titled Zayn, will be released by publishers Penguin Random House on 1 November (16).
The memoir has been described as an "intimate and raw scrapbook of his life", mixing drawings, never-seen-before pictures, personal thoughts, and more, addressing everything from his childhood in England and his rise to teen heartthrob as a member of One Direction.