The Irish actor recalled how he once met The X Factor's Louis Walsh for the try-out before he made it big as a Hollywood star.
Farrell told Yahoo: "So I was on a dance floor in Dublin and I was 17, in leather trousers and a rubber T-shirt - I'll spare no embarrassing details - when Louis Walsh came up to me and said, 'I'm forming a band, they're going to be huge, do you want to be in it?'
"I said, 'Yeah', so I went to an audition the next day and there were 150 lads outside the door with various spray-tans, tight T-shirts, etc.
"I went in and sang 'Careless Whisper' twice... they asked me to sing it again because they couldn't believe how shocking I was!"
Boyzone were eventually formed in 1994 with Ronan Keating, Stephen Gately, Keith Duffy, Shane Lynch and Mikey Graham making the final lineup, while Farrell had his first TV acting gig in 1998's Ballykissangel.
Colin Farrell currently stars in the remake of Total Recall opposite Jessica Biel and Kate Beckinsale.
Watch a clip from Total Recall below: