The singer left the group during a tour in 2015 and later revealed he was really unhappy being part of a boy band.
"We were sad, obviously, that someone had left, but also sad that he was not enjoying it so much that he had to leave," Harry revealed during a chat with Zane Lowe on Apple Music's Beats 1. "I think at the time too, the tour and everything was going so well and everyone had kind of got to this place where everyone was kind of living in a way where they, I think, felt pretty good. It felt like everyone was kind of enjoying it."
"You didn't realize he wasn't enjoying it that much."
Shortly after Zayn split from the band, One Direction announced an indefinite hiatus, and now Harry admits he and his bandmates knew the end was near and they needed a break from one another.
"The last year of it we all kind of knew we were going to stop at the end of that year," he shared. "We'd sit down and have conversations (asking if) everyone (is) good, everyone wants to keep going and that kind of thing."
"There was a part of me, where I felt like all of the decisions I'd made as an adult - that affected my life and what I was doing with my life - had been made as a group. I think there was a part of me that felt like I wanted to make some decisions for myself... I felt like I needed to make some decisions that just affect me."
Harry went on to launch a successful solo career, and his second album, "Fine Line", is due out next month (December).