Sungjae has announced that he will be enlisting in the military on May 11.

On May 3 KST, the BTOB member took to his personal Instagram account to announce the news to his fans himself, leaving a long letter explaining his upcoming plan:

"Hello, it's Sungjae.

First! Thank you so much to all of you Melody [BTOB's fan club name] for wishing me a happy birthday. (I saw all of your social media posts, birthday advertisements, and events!)

I was concerned with how I was going to tell you this, but overthinking it was too much, so I am writing this letter as it seems telling you directly is right.

Many will be surprised by this, but I have decided that I will be enlisting in the military on May 11!

There are people who will be surprised by this sudden news and people who will be concerned, but because of the wonderful treatment I have seen from Melodies, I have confidence that tells me that no matter where I go I will receive love and gallantly serve. I have no concerns at all! It seems I will serve and return without any issues.

Due to the subsequent enlistment of the BTOB members, there is an inevitable break period [in our activities], but because our Melodies will be waiting for us, BTOB will dream about the day we can all meet again and be strong!

There is now only a few days left, but I will communicate with Melodies soon before I go through a live broadcast, and soon the other hyungs will come out [of military service], and  'Mystic Pop-Up Bar' has plans to begin airing soon, so please be patient and the day where BTOB and Melodies can all meet and be together will come soon!

I'm still always really grateful, and in the future as well, please continue to support me! Until the day that I can appear to you all with an even more awesome appearance, please be healthy and spend your days happily. From Yook Sungjae."

Meanwhile, Sungjae will be the fourth BTOB member to fulfill his mandatory service commitments, following members Eunkwang, Changsub, and Minhyuk.

Check out Sungjae's full Instagram post below!