On July 10, the day of his 35th birthday (34th internationally), Heechul wrote on his Instagram page, "Idol School is truly moving. Like the character from 'Great Teacher Onizuka', I will do my best to become a heart-warming teacher. #GTO #GTH #GreatTeacherHEENIM," and shared a video clip of all 41 'Idol School' girls singing the happy brithday song!

Meanwhile, 'Idol School' premieres this July 13 at 9:30 PM KST!

SEE ALSO: In a follow-up interview on a YouTube show, Min Hee Jin admits that she considered methods for acquiring ADOR, but never acted on them

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A post shared by Kim Hee Chul (@kimheenim) on Jul 10, 2017 at 2:54am PDT