King Bhumibol Adulyadej of Thailand, who took the throne of the kingdom once known as Siam shortly after World War II and held it for more than 70 years, establishing himself as a revered personification of Thai nationhood, died on Thursday in Bangkok. He was 88 and one of the longest-reigning monarchs in history, reports The New York Times.

The royal palace said he died at Siriraj Hospital but gave no further details.

King Bhumibol was a unifying figure in a deeply polarized country, and his death cast a pall of uncertainty across Thailand, raising questions about the future of the monarchy itself.

The military junta, which seized power in a coup two years ago, derives its authority from the king. But the king’s heir apparent, Crown Prince Vajiralongkorn, seen by many as a jet-setting playboy, is not held in the same regard as his father.

King Bhumibol spent most of his final years in a hospital, ensconced in a special suite. His portrait hung in almost every shop, and as his health declined, billboards proclaimed “Long Live the King,” signaling widespread anxiety about a future without him. In response, he openly fretted about the people feeling so insecure.

Thais came to see this Buddhist king as a father figure wholly dedicated to their welfare, and as the embodiment of stability in a country where political leadership rose and fell through decades of military coups.

His death ends a reign of 70 years and 126 days, one that few monarchs have matched for longevity. Queen Elizabeth II, by comparison, has ruled Britain for more than 64 years, having surpassed Queen Victoria’s mark in 2015. With King Bhumibol’s death, she becomes the world’s longest-reigning monarch.

King Bhumibol (pronounced poo-me-pon) was an accidental monarch, thrust onto the throne at 18 by the violent death of his older brother in 1946. He fully embraced the role of national patriarch, upholding Thailand’s traditions of hierarchy, deference and loyalty.