The singer/actor, who plays high school teacher Will Schuester on Glee, was convinced he had landed his big break after joining the fivepiece in 2001.
However, Morrison admits he felt miserable singing cheesy tracks and he left the line-up before Lmnt had even released their debut album.
He tells fashion website MrPorter.com, "It's one of the biggest mistakes I've ever made in my life. It was at the height of 'Nsync and the Backstreet Boys, so I really thought I was going to make a lot of money being in a boyband. Singing and dancing to stupid, ridiculous songs didn't feed my soul."