The Queen has become the world's longest reigning living monarch following the death of the king of Thailand.
King Bhumibol Adulyadej of Thailand had reigned since June 9 1946, and was two years younger than the Queen.
Following his death aged 88, Elizabeth II takes up the position as the longest serving current head of state on the planet.
But she is unlikely to acknowledge such a record, particularly as the Thai people are grieving for their revered head of state.
King Bhumibol Adulyadej had been in poor health for a number of years and was rarely seen in public.
The Royal Palace said the king's health had deteriorated until he passed away peacefully on Thursday at Bangkok's Siriraj Hospital, where a large crowd had been holding a vigil.
Prime Minister Theresa May and Foreign Secretary Boris Johnson joined leaders around the world in paying tribute to the monarch, whose death will be marked with a one-year mourning period by Thai government officials.
Saddened by the death of His Majesty King Bhumibol Adulyadej. I offer the people of Thailand my deepest condolences: https://t.co/QJjgre0wC2
-- Boris Johnson (@BorisJohnson) October 13, 2016
May said: "His Majesty guided the Kingdom of Thailand with dignity, dedication and vision throughout his life. He will be greatly missed.
"Our thoughts are with the people of Thailand at this difficult time."
The Queen is already the longest reigning monarch in British history. At around 5.30pm on September 9 2015, she overtook her great-great-grandmother Queen Victoria, having reigned for 23,226 days, 16 hours and some 30 minutes.
However, she has some way to go before she becomes the world's longest reigning monarch ever. King Sobhuza II of Swaziland, who died in 1982, holds this title. He was just four months old when he became king and ruled for 82 years and 253 days.
The longest reign of any monarch of a large country in European history belongs to Louis XIV of France - who was also known as Louis the Great, or the Sun King. His reign lasted for 72 years and 110 days, from 1643 to 1715.