Britain's Queen Elizabeth II is now the world's longest reigning monarch after the death of King of Thailand Bhumibol Adulyadej who reigned for more than 70 years.
Adulyadej, who died yesterday aged 88, ascended to the throne in 1946 and reigned for more than 70 years and four months.
Britain's 90-year-old Queen Elizabeth II ascended to her throne in 1952 aged 25 on the death of her father King George VI and has reigned for 64 years and eight months so far.
She, however, has some way to go before she becomes the world's longest reigning monarch ever.
King Sobhuza II of Swaziland, who died in 1982, was only four months old when he became king. He ruled for 82 years and 253 days.
The Queen is already the longest-serving British monarch in history, having surpassed Queen Victoria's tally of 63 years and 216 days last year.
Prime Minister Theresa May joined other world leaders in paying tribute to Adulyadej, whose name means "strength of the land, incomparable power".
"His Majesty guided the kingdom of Thailand with dignity, dedication and vision throughout his life. He will be greatly missed," May said.