Published Friday, 06 July 2012
Niall Horan was was filmed on his return home to Ireland. (© Getty)
The 18-year-old from Mullingar used a bad word as he walked past a group of girls at Dublin airport on Monday.
"Remember the last time I walked out here?" Horan asked the teens, before using an expletive.
The outburst was filmed on a mobile phone by a fan who did not seemed fazed by the bad word, and kept talking to the singer.
Horan went on to give a happy birthday message into the camera and the video was later uploaded to YouTube.
But the teen later took to Twitter to apologise for his foul-mouthed rant.
"But I understand that it's not a word I should be using at all," he added.
The fans who uploaded the video also leapt to his defence, describing his expletive as "banter".