The Queen was the longest reigning monarch in British history and the longest still-serving sovereign in the world.
She overtook the previous British record set by her great-great-grandmother Queen Victoria at around 5.30pm on September 9 2015, at the age of 89, having reigned for 23,226 days, 16 hours and some 30 minutes.
It was a significant milestone, but she was matter-of-fact about the achievement of being on the throne for more than 63 years and 216 days.
As she thanked the nation for its kind messages on the landmark day, she admitted that the royal record was “not one to which I have ever aspired”.
“Inevitably a long life can pass by many milestones. My own is no exception,” she added.
At that time of year, the Queen was usually enjoying her much-loved annual break at Balmoral, but she was eventually persuaded to carry out duties to mark the occasion.
With the Duke of Edinburgh at her side, she spent the day travelling 40 miles on the railway with Scotland’s First Minister Nicola Sturgeon, starting at Edinburgh’s Waverley station, stopping off at Newtongrange in Midlothian before carrying on to the Borders town of Tweedbank.
The Queen, who was wearing a brooch which belonged to Victoria, delivered her short speech at her last stop, demonstrating her business-as-usual approach at the end by saying: “So now to the business in hand. It is my very happy duty to declare the Borders Railway open.”
Previous record-holder Victoria was only 18 when she became queen and reigned for 23,226 days, 16 hours and 23 minutes, according to the archivists at Buckingham Palace.
The milestone was tinged with sadness for the Queen, who acceded to the throne at the age of 25, as the calculation of her time as monarch was linked to the death of her beloved father, George VI.
Earlier in her reign, in May 2011, she overtook George III, who reigned for 21,644 days, in March 2008 passed Henry III, and, in June 2002, Edward III’s 50 years and 148 days on the throne.
She marked her Silver, Golden and Diamond Jubilees, and in February 2017 and without much fanfare, was the first British monarch to reach a Sapphire Jubilee – 65 years on the throne.
In February 2022, the Queen became first British sovereign to achieve a momentous Platinum Jubilee of 70 years, with millions taking to the streets in June during four days of national commemorations.
She became the world’s longest-reigning living monarch in October 2016 when the previous record-holder, King Bhumibol Adulyadej of Thailand, died after ruling for 70 years.
But she was not the world’s longest-reigning monarch ever – King Sobhuza II of Swaziland, who died in 1982, held this title.
He was just four months old when his father died, and, although his grandmother ruled as Queen Regent for more than two decades, he is considered by some to have technically been king for 82 years and 253 days.
In July 2020, the Queen reached 25,000 days on the throne, spending the day privately at Windsor amid the pandemic.
Elizabeth’s lengthy reign and advanced age brought with it other milestones.
She was the oldest British monarch in history, but was not keen on being reminded of this.
She overtook both Victoria and George III, who were each 81 when they died.
The Queen was also the world’s oldest living head of state.
She also held the world record for the most currencies featuring the same individual, and was the wealthiest queen, with a fortune estimated at around £365 million.