The Queen of England's diary is more hectic than most – but this week's visit by Ireland's President Michael D. Higgins is particularly momentous as it is the first ever visit of an Irish head of state to the U.K..
Higgins, a poet and former academic who is so unassuming that he has been spotted standing in line at ATMs in the center of Dublin, is returning a visit made by the Queen in 2011 - which in itself was groundbreaking as the first time a British monarch had been on Irish soil in a century.
The exchange of visits highlights how far relations between the two countries have progressed since the end of the violent "Troubles" in Northern Ireland in 1998 which saw more than 3,000 people killed. The Queen's cousin, Lord Louis Mountbatten, was killed in 1979 when republican terrorists planted a bomb on his boat.
Higgins' visit will be attended with huge pomp and circumstance. He will first meet the Prince of Wales at the Irish embassy on Tuesday, before going to Windsor to meet the Queen and attend a state banquet.On Wednesday, he will have lunch with Prime Minister David Cameron and speak in the House of Commons.
Enda Kenny, Irish Taoiseach (Prime Minister) told the BBC "this was unthinkable 20 years ago." Indeed, one of the most significant dinner guests on Tuesday is Martin McGuinness, the deputy First Minister of Northern Ireland and former commander if the terrorist Irish Republican Army which waged a long bombing campaign in Northern Ireland and the mainland.
"It's a formalization of Anglo-Irish relations having reached a point of maturity," Roy Foster, professor of Irish history at Oxford, told CNBC.
"There was the running sore of Northern Ireland making the relationship difficult, particularly when (Irish political party) Fianna Fail was in power."
Fianna Fail has historically supported reunification of Northern Ireland with the rest of the Irish land mass.
The recent row over amnesties granted to republicans suspected of crimes including the Hyde Park bombing, shows how an emotive and tense mutual history can still threaten good relationships between the two countries.
Sinn Fein has emerged as one of the most important political parties in Ireland, after broadening their scope beyond the North and taking a seat in the power-sharing government.
The U.K. and Ireland are still both in the process of recovering from the credit crisis, driven by an overleveraged banking sector, and, in certain cases, by reckless lending by the same banks.
Ireland's downturn was much more dramatic than the U.K.'s -- it has only just emerged from a international bailout program -- and the debate over how effective its recovery is progressing continues.
Higgins' visit coincides with increased focus on the possibility Scotland may become independent from the rest of the U.K. If Scotland leaves, it will be watched with interest in Northern Ireland, which has some powers devolved from the central U.K. government.