Queen Elizabeth became the longest-reigning monarch in British history yesterday - breaking Queen Victoria's record on the throne.
She has reigned for more than 23,226 days.
Yesterday she admitted that the milestone was "not one to which I have ever aspired".
She added: "Inevitably a long life can pass by many milestones. My own is no exception. But I thank you all and the many others at home and overseas for your touching messages of great kindness.''
She is believed to have passed Victoria's record at around 5.30pm but the exact moment she became queen is hard to calculate as George VI died in his sleep in the early hours of the morning.
At this time of year, the queen is usually enjoying her much-loved annual break at Balmoral in Scotland, but she broke from her holiday to carry out duties to mark the historic occasion.
The 89-year-old monarch, with Prince Philip at her side, spent the day travelling 60km on the railway with Scotland's First Minister Nicola Sturgeon.
She delivered her short speech at her last stop, Tweedbank, demonstrating her business as usual approach at the end by remarking: "So now to the business in hand. It is my very happy duty to declare the Borders Railway open." The milestone is tinged with sadness for the Queen as the calculation of the length of her reign is linked to the death of her father George VI.