Thais mourn after learning of the death of Thailand's King Bhumibol Adulyadej on Oct. 13, 2016 in Bangkok, Thailand.
King Bhumibol, the world's longest reigning monarch, died at 88 in Bangkok's Siriraj Hospital.
Bhumibol had been king since 1946 and his succession could be a tough test for Thailand, where the government is run by a military junta and where Crown Prince Vajiralongkorn has not earned the same respect as his father.
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The future king of Thailand Bhumibol Adulyadej, stands with his mother, princess Srinagarindra, elder sister princess Galyani Vadhana, left, and brother prince Ananda Mahidol in Switzerland in 1934.
Bhumibol came to the throne in June 1946 at the age of 18 after the mysterious shooting death of his older brother, King Ananda.
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King Bhumibol Adulyadej of Thailand poses with his fiancee Sirikit Kitiyakara in 1950.
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Queen Sirikit and King Bhumibol are welcomed by Queen Elizabeth II and Philip, Duke of Edinburgh, upon their arrival in the United Kingdom in 1960.
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Thai King Bhumibol rides on a horse during his visit to a hilltribe village in 1969. The king was working on a project to help the hilltribe people replace their opium crops with viable alternatives in northern Thailand.
Despite being held in great reverence, the king waded through rice paddies and trudged up hillsides to improve life for Thailand's have-nots.
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King Bhumibol and Queen Sirikit of Thailand attend a reception at Wellington Town Hall at the start of their eight-day tour of New Zealand in 1962.
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King Bhumibol and Prince Vajirlongkorn play saxophones in 1965. King Bhumibol was an accomplished saxophonist and jazz music composer who once shared a stage with Benny Goodman. He continued to play regularly until well into his 70s.
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Thai King Bhumibol greets one of his loyal subjects in the central region of Thailand.
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King Bhumibol and Queen Sirikit admire a statue of Paolina Borghese at the Borghese Museum In Rome.
Thai King Bhumibol Adulyadej and Queen Sirikit meet with leaders of a military coup in Bangkok on Sept. 19, 2006.
Although Bhumibol was a constitutional monarch with no formal political role, he was widely regarded as a unifying figure in Thailand and a symbol of continuity for a population that has lived through a string of governments ousted by military coups.
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Thai King Bhumibol Adulyadej lights a candle in honor of his father, Prince Mahidol Adulyadej, before his departure from Siriraj Hospital after recovering from spinal surgery in Bangkok on Aug. 4, 2006.
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Thai King Bhumibol Adulyadej and Queen Sirikit attend a launching ceremony for a new patrol ship at the Thai Royal Navy Shipyard in Bangkok in 2007.
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King Bhumibol and Queen Sirikit review the honor guard during the trooping of the colors to honor the King's 80th birthday at the Royal Plaza on December 2, 2008, in Bangkok.
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Wellwishers wave flags and pray as Thailand's King Bhumibol Adulyadej leaves Siriraj hospital in Bangkok on Sept. 15, 2014.
The king spent most of the last decade in a hospital for a variety of ailments related to old age.
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