Queen becomes world's longest reigning monarch after Thai King dies
The King of Thailand has died at the age of 88 - making the Queen the world's longest reigning living monarch.
King Bhumibol Adulyadej of Thailand had reigned since June 9 1946 and was two years younger than the Queen.
A statement from the Thai palace said: "His Majesty has passed away at Siriraj Hospital peacefully."
His son and heir, 63-year old Crown Prince Maha Vajiralongkorn, is expected to become Thailand's new king.
King Adulyadej - whose name means "strength of the land, incomparable power" - had been in poor health for some time and spent most of the past six years in hospital.
He was re-admitted in May 2015 and was last seen in public in January, when he spent several hours visiting his Bangkok palace.
The Thai prime minister asked the Thai people to not hold any festivities for the next 30 days.
He said the country would go into mourning for one year starting Friday.
King Adulyadej came to the throne in 1946 after the still unexplained gunshot death of his elder brother, 20-year-old King Ananda Mahidol whowas also known as Rama VIII.
His popularity stemmed partly from his long reign, but he was also viewed as a pillar of stability.
Strict lese-majeste laws banned any criticism of him or the Thai royal family.
In August 2015, a man was sentenced to 30 years in prison by a Thai military court for insulting the country's monarchy on Facebook.
Following his death, 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.
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.