South Korean pop star and actress Sulli — best known as a founding member of the girl group f(x) and as the star of popular TV dramas and films — has died at age 25.

The Associated Press reported Monday the singer was found dead at her home in Seongnam (just south of Seoul) after her manager reported the performer hadn’t answered phone calls for hours. A cause of death has not been reported. Local police do not suspect foul play, nor did they find a suicide note.

“The investigation is ongoing and we won’t make presumptions about the cause of death,” Kim Seong-tae, a Seongnam Sujeong Police Department, told the AP, while a statement from Sulli’s management, SM Entertainment, indicated the agency found her death “very hard to believe and sorrowful.”

Sulli (real name Choi Jin-ri) began her career in 2009 as one of the original members of the pop group f(x), assisting the group’s rise to fame via four No. 1 albums and four No. 1 singles in their home country. She later left the group in 2015 to pursue a solo career, and released her debut single “Goblin” earlier this year.

In addition to singing, Sulli led the popular TV drama To the Beautiful You before appearing in major Korean movies like The Pirates (2014), Fashion King (2014), and Real (2017).

Sulli also made headlines for her outspoken views on feminist issues in traditionally conservative Korean society, including her advocation for the no bra movement. She also recently appeared on a regional television show to speak out against the backlash she’d received over her lifestyle.