Kim Jonghyun, the lead singer of top South Korean pop group SHINee, was found dead Monday evening. He was 27.

Widely known simply as Jonghyun, Kim was found unconscious at an apartment in Seoul. He was taken to the hospital but did not regain consciousness, according to Korean news agency Yonhap.

The discovery of his body in Gangnam district’s Cheongdam quarter followed a report to police by his older sister that Kim was behaving erratically.

Without identifying their sources, several local news outlets said that Kim committed suicide. Others added that he was killed by carbon monoxide poisoning after heating up charcoal in the apartment.

A police briefing said that he sent a text message to his sister that sounded like a suicide note. “I’ve had a hard time. Please let me go and say that I did a good job. This is my last word,” the message said, according to the police. SM Entertainment, Kim’s management group, has not yet offered any statement.

The world of Korean celebrity is notoriously high-pressure. On one hand, performers are tightly managed by their agencies and labels. On the other, they are often held to absurdly high standards of behavior and are subject to blistering social media commentary.

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SHINee, a five member boy band, was formed in 2008 by SM Entertainment. It became known as one of the most skillful in terms of vocals and dance, and was hugely popular and influential both in music and fashion.

The group recorded six albums for the Korean market and five for Japanese fans. “Five,” its fifth Japanese album, was released in February this year. It embarked on the SHINee World Tour to promote it, playing to 320,000 fans at 25 concerts in 10 cities. The group’s most recent concert was 8 days ago.

The group appeared in two films – “I AM,” from 2012, and 2015 documentary “SMTown: The Stage” – as well as in numerous reality TV shows. The band had been named as honorary ambassadors of Gangnam in 2013.