World's longest-reigning monarchs

Britain's Queen Elizabeth II (L) sits next to Prince Philip, Duke of Edinburgh (R), on the throne in the Chamber of the House of Lords as she reads the Queen's Speech.

On September 9, Queen Elizabeth II will become Britain's longest-reigning monarch having been on the throne for 63 years and 216 days.
Elizabeth, 89, will surpass the record of queen Victoria. However, the world's longest-reigning monarch is the king of Thailand, who marked the 69^th year of his reign in June.
Following is a list of the current longest-reigning heads of state:

• THAILAND: King Bhumibol Adulyadej, 87, acceded to the throne on June 9, 1946 after his brother died in mysterious circumstances. He was crowned in 1950 after completing a degree in Switzerland. A constitutional monarch, Bhumibol is a revered moral authority in a country subject to political instability. His health is poor however, and the palace revealed in early August that he had recently been treated for "water on the brain" and a chest infection.

• BRITAIN: Queen Elizabeth II, born on April 21, 1926, inherited the throne on February 8, 1952 following the death of her father, king George VI. On September 9, Queen Elizabeth's reign is to surpass that of her great, great grandmother queen Victoria, who was on the throne from 1837 until 1901. Queen Elizabeth is queen of 15 other Commonwealth realms.

• BRUNEI: Sultan Hassanal Bolkiah, 69, is one of the richest people on the planet. Bolkiah has reigned over the small enclave on the north coast of Borneo since his father abdicated in October 1967. Brunei has sizeable petroleum reserves.
• OMAN: Sultan Qaboos, 74, took the throne on July 23, 1970.

• DENMARK: Queen Margrethe II, 75, became head of Europe's oldest kingdom on January 14, 1972 following the death of her father, Frederik IX.

• SWEDEN: King Carl XVI Gustaf, 69, succeeded his grandfather, Gustaf VI Adolf, in September 1973. He and Queen Margrethe are first cousins.