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.