The 18 year-old winger has played his final game for Daejon ahead of moving to England and beginning the next stage of his career with Brighton.
After playing Yun in their 0-0 draw at home to Gimcheon Sangmu in the K-League this week, Hwang said afterwards: “I think he is still young and has a lot of potential for growth.
“I wanted to give him more time, but I was a little disappointed with his condition.
“I congratulate him on his advancement to Europe, and I hope he becomes a world-class player, not just in Korea.
“The timing is unfortunate, but I think he did his best in Daejeon. I will cheer him on, so I hope he shows a good performance.”
Yun will do preseason with Brighton before a decision is made about a potential loan move away for the new season.