Thailand’s King Bhumibol Adulyadej, 88, the world’s longest-reigning monarch, died in hospital on Thursday, the palace said in an announcement.
No reason was given for the death of the king, who was strongly revered in Thailand, but he had been in ill health for some time.
“His Majesty has passed away at Siriraj Hospital peacefully,” the palace said, adding he died at 15:52 (0852 GMT).
Crowds had gathered outside the hospital where the king was being treated to pray for his recovery.
But he had been in poor health for years and was last seen in public in January.
A period of mourning of a year has been announced for government officials, and flags will fly at half mast at all government buildings and schools for 30 days from Friday.
His son and heir apparent, the 63-year old Crown Prince Maha Vajiralongkorn, is expected to become Thailand’s new king.