The Queen has thanked well-wishers for their "touching messages of kindness" as she officially becomes Britain's longest-reigning monarch.
As of 5.30pm Queen Elizabeth II surpassed the record set by her great-great-grandmother Queen Victoria, having reigned for 23,226 days, 16 hours and approximately 30 minutes - or 63 years and seven months.
The exact moment the Queen becomes the longest-reigning sovereign is unclear, as her father, George VI, passed away in the early hours of 6 February 1952, but his exact time of death is unknown.
Celebrating the Queen's record reign - in pictures
The Queen spoke briefly in the Scottish Borders earlier today, saying the title was "not one to which I have ever aspired", and it was business as usual for the monarch today, who was in Soctland to officially open the new £294m Scottish Borders Railway.
Dressed in turquoise, the 89-year-old monarch told the gathered crowds: "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."
Scottish First Minister Nicola Sturgeon, who was also present at the opening, said it was a "historic day", and praised Queen Elizabeth's “dedication, wisdom and exemplary sense of public service”.
MPs also took time out in the Commons to pay tribute to the Queen. Prime Minster David Cameron said she had been a "rock of stability" in changing times, and that her reign had been the "golden thread running through three post-war generations".
Acting Labour leader Harriet Harman said the Queen was "admired by billions of people all around the world", while in the House of Lords, leader Baroness Stowell said the Queen had served the country with "unerring grace, dignity and decency".
