Jongseob

From December 2016 to April 2017, Jongseob participated in the competition show K-pop Star 6: The Last Chance and won as part of the duo, Boyfriend, with Park Hyeon Jin. Following the show's conclusion, the duo signed a trainee contract with YG Entertainment. However Hyeon Jin left the agency shortly after due to differences in musical style while Jongseob would continue on as a trainee.

The following year, he joined YG Treasure Box in Group C. However, he was eliminated in Episode 9. In late August, it was reported that Jongseob would be debuting as a member of FNC Entertainment's upcoming boy group after signing a contract with the agency.