Jeong In Seong

Along with Seungjun, he was a former Big Hit Entertainment trainee where they both trained with the members of the boy group BTS. Upon moving to FNC Entertainment, he appeared as one of the trainees in its reality show Cheongdam-dong 111 along with Heejun in 2013. Before debuting with KNK, he was a backup dancer for the live performances of BESTie's "I Need You".

In January 2024, he was revealed as a contestant on Mnet's reality survival show Build Up : Vocal Boy Group Survivor. On December 19, 2024, it was reported that Jeong In Seong was casted in the musical "일기쓰는남자" as Lee Moji and would appear on stage on February 18-22, 2025 at Gwangmyeong Civic Center Grand Concert Hall.