Jonghyun was taken to the hospital in Seoul where he was later pronounced dead after being found unconscious in his apartment - reportedly after inhaling toxic fumes from coal burning on a frying pan.
Jonghyun had also branched out on a successful solo career in 2015, performing two solo concerts in Seoul just this month, but he was the only original member of SHINee to participate in the band's reformation earlier this year, which coincided with their fifth album release.
The text then caused his sister to alert Gangnam Police that Kim Jong-hyun's life may be in danger.
The five-member SHINee is one of the best-known K-pop groups globally and has enjoyed a huge following across Asia and beyond since their debut in 2008. His last public appearance was at a solo concert titled Inspired on December 9 and 10 in Seoul.
Toronto billionaire, wife found dead; Police call deaths 'suspicious'
Homicide detective David Hopkinson said: "The circumstances of their death appear suspicious and we are treating it that way". Sherman has also been an active philanthropist, including donating $50 million to the United Jewish Appeal.
Kim spent almost a decade in his leading role as one of five members of SHINee, one of the most popular boy bands in the country, as well as a solo artist. He was 27 years old. SHINee have been called the Princes of K-Pop due to their complex dance routines and incredible live vocals, earning huge hits with songs including Sherlock, Replay, Ring Ding Dong and Dream Girl.
Kim's fans will be able to pay respects at the funeral hall of Asan Medical Center in Songpa-gu, Seoul.
South Korean pop culture has conquered a large part of Asia over past decade with its K-pop stars topping charts across the region and its TV dramas enjoying huge popularity.