Tongan King Taufa'ahau Tupou IV, a towering figure in the tiny Pacific Island nation for four decades, has died in a New Zealand hospital, ending one of the longest reigns of modern times, Tonga's government announced Monday. He was 88. «The sun has set in the Kingdom of Tonga,» the government said in the formal announcement of his death. Tupou's death came at the end of a long but unspecified illness in a hospital where the king had spent most of the past several months, the Associated Press reported. Acting Prime Minister Viliami Tangi said the king died shortly before midnight Sunday New Zealand time (1200 GMT). Crown Prince Tupouto'a, 57, who will take over the king's duties, took the vows in the Tongan Constitution in front of the nation's chief justice on Monday in the capital, Nuku'alofa, said Lord Chamberlain Hon. Fielakepa. He has taken the name King Taufa'ahau Tupou V, said Fielakepa, a member of the Tongan nobility assigned to serve the monarch. Under Tongan tradition, mourning will continue for nearly a year, with special rituals 10 days and 100 days after the king's burial in Tonga. A coronation ceremony for the new king will take place after that.