The King of Spain begins a state visit to the UK that could see him bring up the controversial issue of Gibraltar - just like his father former King Juan Carlos.
King Felipe VI and his wife Queen Letizia will be officially greeted by the Queen and Duke of Edinburgh during a ceremony of military pomp and pageantry on Horse Guards Parade.
During their three-day visit the Spanish monarch and his wife will be dined during a Buckingham Palace state banquet, with Prince Harry and the Duke and Duchess of Cambridge expected to attend, visit the Palace of Westminster, where the King will address parliamentarians, and on Thursday Felipe will meet Prime Minister Theresa May at Downing Street.
But the backdrop to the visit are strained relations between Spain and the UK over the sovereignty of Gibraltar that has come to the fore because of Brexit.
Simon Manley, Britain's ambassador to Spain, was questioned by journalists in Madrid last week and when asked if Felipe could talk about the British overseas territory, in his Westminster speech, he replied it was a possibility.
Last September, Felipe used his address to the UN General Assembly in New York to call for a negotiated handover of "the Rock".
The ambassador, who has travelled to the UK for the visit, went onto say the King's father broached the same subject when he made a state visit to Britain when monarch in 1986.
Juan Carlos, in the first address by a foreign monarch to both houses of Parliament, said he was looking forward to a resolution to the dispute over Gibraltar and that dialogue, underway at the time, was "a step forward".
Spain has a long-standing territorial claim on Gibraltar, which has been held by the UK since 1713, but Mrs May has previously insisted that Gibraltar's status will not be up for discussion during exit talks from the EU.
The Spanish state visit 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 Duke of Edinburgh, who recently spent a short spell in hospital, is due to accompany Felipe as he inspects the Guard of Honour, the 1st Battalion Irish Guards, on the Horse Guards Parade ground.
Security will be tight for the royal carriage procession along The Mall in what will be the first state visit to take place since the terror attacks in Manchester and London.
Glamorous Queen Letizia is the former TV anchorwoman who became Spain's first ''commoner Queen'' while the King has been billed as representing a ''new era of hope'' for Spain's monarchy.
The 49-year-old, who is a towering 6ft 5in tall, came to the throne three years ago when his father Juan Carlos, now 79, abdicated after 40 years as king following ill health and damaging scandals.