Reuters wrote Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch who was seen as head of an institution central to Thai identity and as a father-figure to the nation, died in a hospital on Thursday, the palace announced. He was 88.

King Bhumibol reigned for seven decades after ascending the throne in 1946. His loss will be deeply mourned in Thailand, where he was regarded as a pillar of stability during decades of political upheaval and rapid development.

"His Majesty has passed away at Siriraj Hospital peacefully," the palace said, adding he died at 15:52 (4.52 a.m. ET).

Prime Minister Prayuth Chan-ocha addressed the nation shortly after the announcement of the king's death to say an heir to the throne had been designated since 1972 and that the government would inform parliament of the choice. Prayuth did not identify the heir but King Bhumibol designated Prince Vajiralongkorn, 64, the heir apparent when he invested him as the crown prince in 1972.

The palace did not give a cause of death but he has been sick in the hospital with various ailments for much of the past year.