Hara was found dead at her home Sunday in South Korea. Authorities have not released the cause of death ... it's still under investigation.

Hara reportedly attempted suicide in May and was hospitalized for a time. It occurred after an ex-boyfriend tried blackmailing her, threatening to release a sex video.

Her last post on Instagram was Saturday ... a pic of her in bed with the caption, "Good night."

Hara's death comes a month after another former K-Pop singer, Sulli, was found dead and authorities suspect that was suicide.

Hara joined Kara in 2008. She released a solo hit in 2015 and released another song -- "Midnight Queen" -- a few weeks ago.

Hara was 28.