South Korean pop star Sulli was found dead at 25. Police said she was suffering from a “severe depression”.

A former member of the main group of South Korean girls, f (x), who spoke out against cyberbullying, was found dead on Monday, police said. The body of Choi Jin-ri, better known by his stage name, Sulli, 25, was found at his home in Seongnam, south of the capital, in Seoul, police said.

“Her boss went to her home after not being able to contact her since her last call last night,” police said in a statement. Sulli, 25, was struggling with severe depression, the police said. They did not give more details.

Sulli debuted with the five-member f (x) in 2009. He became one of the most popular girls groups in South Korea and helped to boost the global fashion of K-pop. Sulli left the band in 2015 and began a career as a singer and solo actress.

He became famous in 2005, at the age of 11, playing Princess Seonhwa of Silla in the dramatic SBS Ballad of Seodong. Sulli debuted as a member of f (x) with fellow bandmates Victoria, Amber, Luna and Krystal in September 2009 with the single La Cha Ta.

The star born in Busan had a phenomenal success during one season with the group of girls. Pinocchio (Danger), Electric Shock and Hot Summer are some of his most successful songs.

Sulli’s last post on Instagram was published a day ago, when he shared a video of a Stretch Angels gift. Most recently, he appeared on a TV show during which K-pop stars shared their experiences with malicious comments online.