Britain's Queen Elizabeth II will make history later today by becoming Britain's longest-reigning monarch.
The Queen will break the record previously held by her great-great-grandmother Queen Victoria whose reign, according to Buckingham Palace, lasted for 23,226 days, 16 hours and 23 minutes - or around 63 years and 216 days.
Princess Elizabeth became Queen when she was only 25 years of age, on 6 February 1952, after her father died.
It is thought Queen Elizabeth II will break Queen Victoria's record at around 5.30pm this afternoon, but it's difficult to pinpoint a precise time because the exact moment of her father's death is not known.
However, the most important event for Ireland in relation to the Queen's reign was her visit to these shores back in 2011, the first made by a British monarch to these shores since King George in 1911.
She spent three nights in Ireland, staying at the Farmleigh State Guest House in the Phoenix Park.
The defining moment of the visit came in Dublin Castle when at a State Dinner, Queen Elizabeth rose and delivered a speech which she had written along with her private secretary which began in Irish and noted the progress that both nations made.
It was a defining and historically important changing point for British and Irish relations.
The history of the UK's longest reigning monarch
It is inevitable that comparisons will be made between the two women, and some experts argue Queen Victoria would become an ideal role model for her great great granddaughter.
Historian Kate Williams said: "When Elizabeth came to the throne, yes she was 25, yes she was a mother of two.
"But yet, people were still rather dubious about a female: they said she's just a woman, it was the 50s, it was very sexist.
"But actually it was very important for her to have the example of Victoria, saying a woman can do the job in the 19th century - I can do the job now."
There are not any large scale national events planned to mark this milestone, and members of her family will not be seen to celebrate the moment.
The Queen herself has said she doesn't want any fuss, and expects it to be business as usual, treating the day like any other.
It is understood this is partly out of respect for Queen Victoria, but also because large celebrations are being planned for Her Majesty's 90th birthday next year.
But the Queen, who is currently on her summer holiday at her private Scottish home of Balmoral, will travel to Edinburgh and then down to the Borders to open a new railway line.
Accompanied by the Duke of Edinburgh, she will board a train at Edinburgh Waverley station pulled by the steam locomotive the Union of Africa, taking a two hour journey to Tweedbank, where she is expected to be met by large crowds.
There has been speculation that the Queen may make a rare public speech to mark the moment.
Buckingham Palace hasn't yet released the Queen's full programme for the day, but if she does speak publicly it's likely to focus on the railway line rather than her own achievements.
It comes as a poll suggests the monarchy and the Queen remain as popular as ever.
The results from Sky Data found that 70% of people think Britain should remain a monarchy forever, with 61% saying they did not think the monarchy was a waste of money.
Some 58% also said they trusted the Queen more than most politicians.