Former H.O.T main vocalist Kangta took to his Instagram to commemorate the occasion, referring to his old group as the idol industry's trilobite (fossils of one of the oldest living creatures on earth)! Sure, H.O.T are an old, legendary group, but are they trilobite old? Kangta's full post read, "21st anniversary! Congratulations, everyone hehe. I would like to thank everyone who has been with us for the last 21 years. #H.O.T #TheIdolIndustry's #Trilobite."

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Anyway, Happy 21st anniversary, H.O.T!

21주년!축하해 다들 ㅎㅎ21년 함께와주신 모든분들 감사합니다 ㅎ #H.O.T.#아이돌계#삼엽충

A post shared by 강타 (@an_chil_hyun) on Sep 6, 2017 at 8:25pm PDT