One Direction became an international sensation when they got their start on the UK’s "The X Factor," but in 2015, after a wildly successful few years, the band split up. Post-breakup, ex-1D member Harry Styles gained quite a lot of traction in his solo career, but he maintains a good relationship with most of his former bandmates, including Niall Horan.
While still in One Direction, Styles and Horan forged a very special bond through their common tastes in music; Horan told British GQ in 2020, "We were both heavily influenced by 1970s English and American rock and would always be sharing bands with each other, showing each other songs." Nowadays, the pair support each other's solo careers.
When Styles released his album "Fine Line," Horan was one of the first to praise and text him saying, "All your influences are there, you've just smashed it, nailed it." The two ex-bandmates are always quick to congratulate each other on new releases, and also occasionally pay tribute to their time in 1D, with styles doing so in 2020 and Horan following suit.