On Instagram, Koo expressed experiencing profound grief and intense pain.
Hsu, a leading figure in the Mandarin-speaking world, reportedly fell ill and passed away while visiting Japan with her family.
The sudden passing of the 48-year-old star deeply impacted the entertainment industry. She was renowned for her role in the popular 2001 TV series Meteor Garden, which garnered widespread success in Asia.
"My angel returned to heaven on 2 February, 2025… At present, I am enduring overwhelming pain," Koo shared in a recent Instagram post.
In the post, known as DJ Koo, he also requested privacy for his grieving family.
Koo pleaded, "Please, let Hsu rest in peace," after facing undue scrutiny during this sorrowful time.
Koo conveyed his intention to entrust all of Hsu's hard-earned assets to his mother-in-law to secure their protection for their children's future, emphasizing legal measures to safeguard their inheritance until they come of age.
Hsu and Koo first crossed paths in 1998 when she, along with her sister, hosted a popular variety program, and Koo, a member of the K-pop duo Clon, appeared as a guest.
After dating and then parting ways due to management conflicts, Hsu later married Chinese businessman Wang Xiaofei, with whom she had two children. Following a decade of marriage and a contentious divorce in 2021, Hsu and Koo reunited in 2022.
Hsu's unexpected passing shook fans across Asia, where Meteor Garden, based on the Japanese manga Boys Over Flowers, gained immense popularity through localized broadcasts.
Hsu, known for hosting Taiwanese variety shows alongside her sister Dee, rose to fame as part of the pop duo SOS in the 1990s, earning the monikers Big S and Little S.
According to local reports, Hsu's remains were repatriated to Taiwan on Thursday.