K-pop star Moonbin, member of boy band Astro, died at 25.
He was found unresponsive in his apartment in Seoul's Gangnam neighbourhood.
The cause of death was not disclosed by his music label, Fantagio.
Moonbin was a member of the group Astro and also performed with a subgroup called Moonbin & Sanha.
He joined the Fantagio label's trainee program at a young age and was an actor and model before debuting with Astro in 2016.
Moonbin's sister Moon Sua is also a K-pop singer, performing as part of the girl group Billlie.
The announcement of Moonbin's death prompted an outpouring of grief from fans.
Several other young K-pop stars have died in recent years, including Goo Hara, Sulli, Minwoo, and Jonghyun.
K-pop stars are picked up by agencies at a young age and live under tight control, with their days taken over by gruelling musical and dance training.
Moonbin's music label asked for privacy and for people to refrain from speculative and malicious reports.