The British rocker teamed up with the boyband last month (Feb13) to record new material for their next album, and insists he enjoyed working on a new genre in the studio.
He tells BBC Newsbeat, "It was a really interesting creative process, writing with pretty much the biggest pop band on the planet. It was a very different world and very different process - that was one of the reasons I wanted to do it. I really enjoyed it. I felt like I took so much from doing it.
"I've always said I love pop music and how much I want to write pop music. It's the first time I've ever done anything like that. They do indeed contribute (to the song-writing process)."