The group disbanded after five years in 2015 and the singers embarked on separate solo careers.
“When One Direction split up, I was mortified, I was absolutely gutted,” Tomlinson told The Times in a new interview.
“I was a bit bitter, I suppose because it just felt like another loss to me. But I’ve a better understanding of things now, and there’s not as much anger. It is what it is.”
Asked about Styles’ “ascendance into the biggest star of his generation”, Tomlinson replied: “Well, it’s not a surprise is it? We were always aware that Harry fit that mould, and it’s been an amazing thing to watch.
“Envy? At the start maybe, when I was trying to find my feet, but it’s never healthy to cross-reference your own success with others is it? These days I’m learning to elevate myself in those moments when I have to. I didn’t know how to do that before, but now? Now I know I f***ing can.”
Styles has been by far the most successful solo artist of the former group with three No 1 albums. His most recent, Harry’s House, just won the Grammy Award for Album of the Year and swept the Brit Awards with four wins.
Styles came under fire for his acceptance speech at the Grammys, during which he said “this doesn’t happen to people like me very often”. Music fans were quick to point out that white, cisgender males like Styles have dominated awards ceremonies for decades.
Tomlinson refused to speculate on what his former bandmate meant by the comment, saying: “Only Harry knows what he means there... but we all came from relatively humble beginnings, and now we are where we are.”
Tomlinson is currently promoting the documentary about his second solo album entitled All of Those Voices.
It will be a story of “self-discovery and the courage it takes to be true to oneself,” according to the release.
All of Those Voices is out in select cinemas from 22 March.