Translation:

Heechul said originally, he had prepared to debut as TRAX’s main vocal and not as an idol trainee but at the time, he had a small conflict with an SM official over their differing musical directions and had to write a letter of apology everytime. As such, he was so frustrated, he gave up on debuting as part of TRAX and returned home to Kangwon-do. It was thru the persuasion of TRAX’s members, Jungmo and Jay, and TVXQ’s U-know Yunho and Super Junior’s Donghae that he returned to SM.

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Credits:

Sports Chosun,
Translated by @snxy,
Shared by TVXQ! Express