"Lonely" is the final single by SISTAR. It was released on May 31, 2017 with "Lonely" serving as the single's title track
After announcing the group's disbandment on May 22, Starship confirmed the group will promote on music shows for one final week before their contracts expire on June 4. They performed their goodbye stages on M! Countdown, Music Bank, Show! Music Core, and Inkigayo.