On the March 23 airing of 'Happy Together 3', Heechul was asked if he was really a rebel during his trainee years. 

The idol answered, "I moved from Gangwon-do to Seoul when I was 20-years-old. I always listened to music and I told (staff noona) that I was listening to KISS' music. The noona then told me that I shouldn't listen to that kind of music but listen to Linkin Park and study. So I said, 'Noona, rock music isn't something that you can study.' She yelled at me for talking back and told me to write up an apology. I responded, 'I'm not sorry for anything but I'll do it anyway since you're telling me to'."

SEE ALSO: Park Gyu Young's agency issues a response to her 'Squid Game 3' spoiler controversy

Heechul continued, "I got suspended often. They told me not to come for awhile and I just said ok. I used to live in dorms with Donghae and Yunho. They would ask if I really don't have to go and I said, 'They will call me when they need me'."

Heechul also admitted that he was cocky at the time, and said, "When I think about it now, it makes me cringe."