DY

On October 25, 2018, Jeon Do Yum was introduced as a contestant of Under Nineteen with his moving poster. The poster revealed that he was a part of the performance team. He finished in first place, thus becoming a member and the center of the project group 1THE9.

On April 13, 2019, the group officially debuted with the mini album XIX. 1THE9 officially disbanded on August 8, 2020, following the release of their final mini album Good Bye 1THE9. On May 26, 2021, DY was revealed as a member of Bluedot Entertainment's then upcoming group JUST B.