The formation of Stellar began as early as 2010, originally supposed to be a six-membered group with a former trainee from Japan, but Top Class Entertainment reported that member Kim Gayoung had signed an exclusive contract with the company and would be joining a five-member girl group. Gayoung had gained attention for her appearance on the Viewers' Tour episode of "1 Night 2 Days" and had been cast in the drama series "Poseidon" alongside Top Class Entertainment operator and Shinhwa member Eric Mun. The series was set to air on the SBS network until production halted following the November 2010 Yeonpyeong bombardment incident. The roles were subsequently recast when production was greenlit by KBS a year later. Gayoung was later cast in the 2011 drama "Spy Myung-wol" along with Mun.