The One Direction member had used the obscenity in jest when approached by fans at a Dublin airport earlier this week, calling them a “shower of c**ts.”
After the out-of-context moment was caught on camera and posted online, some fans were offended, prompting the apology.
Horan tweeted, “Really sorry if I caused any offence. It was just banter with fans who I think of more as mates.”
The singer continued, “But I understand that it’s not a word I should be using at all.”