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Chae Yeon communicated to fans about this big decision on her Instagram, writing a letter that relayed her determination to do her best in both DIA and IOI. 

She wrote, "Hello. This is Chae Yeon. You were probably shocked to find out that I have joined DIA again. I worried over how I should communicate the way I feel to you all without any misunderstandings. First, I wanted to personally tell you [about re-joining DIA] but because I couldn't, I just feel regretful and sorry. Because I was a part of the program, debuted as a member of IOI, and received so much love from my fans, I wanted to be sure to be the first one to tell you this news; I wanted to promise you all that I will not neglect IOI promotions. As much as you all love me, I will try to be someone who tries even harder as a member of IOI. Every moment that I get to stand in front of you is always so precious to me. That is why I will continue to give it my all so that I won't hurt or disappoint you. I will always be a Chae Yeon who tries her best. Thank you."

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A photo posted by ??? (@j_chaeyeoni) on May 11, 2016 at 1:18am PDT