The Queen is to finally welcome the King and Queen of Spain to the UK this week for a three-day state visit.
King Felipe VI and Queen Letizia's trip was postponed twice - firstly because of a political crisis in Spain in March 2016 and then again when the rescheduled date clashed with June's snap general election.
The Spanish royals arrive in London on Tuesday, and will be formally greeted by the Queen and the Duke of Edinburgh on Horse Guards Parade on Wednesday.
It is expected to be 96-year-old Philip's last state visit before he retires from public duties after the summer.
Security will be tight for the ceremonial welcome and carriage procession in what will be the first state visit to take place since the terror attacks in Manchester and London.
The royal stay is beginning one day later than is usual, meaning Prime Minister Theresa May will miss Prime Minister's Questions in the Commons to attend the Horse Guards welcome.
Felipe and Letizia, who are staying at Buckingham Palace, will be feted with a grand state banquet in the ballroom on Wednesday evening - with Prince Harry and the Duke and Duchess of Cambridge expected to be attending.
It will be the first time full time royal Harry, who is 32, has taken part in a state visit. On Thursday, he will accompany the royal visitors to Westminster Abbey.
Felipe will lay a wreath at the Grave of the Unknown Warrior and Harry will join them on a short tour of the Abbey, including the Tomb of Eleanor 'Leonor' of Castile - the 13th century Spanish princess who married Edward I.
The state visit is seen as an important step in securing relations with Spain as the UK leaves the EU. The last incoming state visit by a Spanish king - Felipe's father Juan Carlos - was 31 years ago.
William and Harry have a shared history with the King. As youngsters, they holidayed with Felipe, his father King Juan Carlos and their family in Majorca several times in the 1980s. Felipe and Letizia were also guests at the Duke and Duchess's wedding in 2011.
The Cambridges are already viewed as the royal family's Brexit ambassadors, and are setting off on another diplomacy tour next week - heading to Germany and Poland for five days with their children Prince George and Princess Charlotte in tow.
Felipe is is expected to raise the thorny issue of Gibraltar during his stay.
He will deliver an address at Westminster from the Royal Gallery to parliamentarians on Wednesday, and meet Mrs May for talks at Downing Street on Thursday.
Last September, he used his speech to the UN General Assembly in New York to call for a negotiated handover of what Gibraltarians affectionately call 'the Rock'.
"I invite the UK, on this first occasion at the UN after Brexit, to end the the colonial anachronism of Gibraltar with an agreed solution between both countries to restore the territorial integrity of Spain," he declared.