The Prince and Princess of Wales have welcomed President Donald Trump and First Lady Melania to Windsor Castle.
It is the first time in modern history that a serving American president has been accorded the honour of two full state visits to the United Kingdom.
The decision to place Prince William and Catherine at the forefront of the welcome underscores their growing role at the heart of the monarchy.
Prince William met the President last year in Paris at the British Embassy where he said he was doing “a fantastic job.”
Their handshake and smiles are expected to set the tone for a day of high ceremony.
The prince and princess escorted the president and his wife the short walking distance to meet the King and Queen in front of the gable-ended Victoria House.
The unique setting, never used before at an incoming state visit in modern times, is just one of a number of flourishes being added to impress the controversial billionaire-turned politician, who sees the King as his "friend".
Camilla rallied to attend the first engagement of the key diplomatic royal duty after pulling out of the Duchess of Kent's funeral on Tuesday due to acute sinusitis.
With their arrival the occasion formally becomes a state visit, triggering the military spectacle that has for centuries marked Britain’s greeting to visiting heads of state.
The Queen wore a vibrant sapphire blue dress, a matching coat by Fiona Clare and hat by Philip Treacy and a sapphire and diamond brooch.
Pomp and pageantry was out in full force with the scale and spectacle of the military ceremonial on show for Mr Trump unprecedented.
Lining the carriage procession route through the private Windsor estate to the castle were 22 half-companies of personnel from throughout the Royal Navy, the Royal Marines, the British Army and the Royal Air Force.
The King’s Troop Royal Horse Artillery, positioned on the East Lawn and at the Tower of London, will fire a thunderous forty-one-gun salute.
The rolling echo of the guns, once a signal of Britain’s imperial might, will provide a resonant soundtrack of respect and recognition.
The largest Guard of Honour mounted for a state visit in living memory will stand ready to salute the visitors.
Grenadier Guards with their single-button tunics and white plumes will form the front rank. Coldstream Guards with paired buttons and red plumes will stand behind them, and the plume-less Scots Guards will complete the line.
Each soldier’s bearskin cap and scarlet coat will bear silent testimony to a tradition stretching back to the seventeenth century.
At the command of Lieutenant Colonel Storm Green of the Coldstream Guards, the Massed Bands will strike the first notes of the Star-Spangled Banner and God Save the King.
Three immense state colours, each more than ten kilograms of silk, will dip in salute as the anthems rise.
President Trump, escorted by the King, will then inspect the guard, while William and Catherine remain with the First Lady and Queen Camilla, exchanging quiet words as the soldiers stand motionless in the midday sun.
The ceremony, precise to the last footstep, is intended to marry spectacle to purpose: a visible reaffirmation of the partnership between Britain and the United States.
For William and Kate the day will mark a significant milestone.
Although they have represented the Crown overseas and hosted world leaders before, this will be their most prominent role yet in the choreography of such an important full state visit.
Palace officials describe the choice as both historic and deliberate, demonstrating the King’s trust in them as the next generation of the monarchy and placing them at the heart of Britain’s most important.
The visit comes at a moment of renewed strategic cooperation between the two nations. Britain has recently deepened its defence commitments in Europe and ordered a new tranche of American F-35 fighter jets to enhance joint operations.
US military personnel continue to be based at key British installations, while British officers serve alongside American counterparts across the Atlantic.
The ceremonial welcome will highlight those ties. Later in the afternoon the Massed Bands of British and American military musicians will perform the ancient Beating Retreat on the East Lawn, a ritual once used to signal the closing of fortress gates.
That will be followed by the first joint UK–US military flypast ever mounted for a state visit. Two RAF F-35B Lightnings and two US Air Force F-35A jets will sweep over the castle alongside the Red Arrows, a dramatic symbol of shared defence.
As evening falls attention will turn from the parade ground to the candlelit grandeur of St George’s Hall, where the King will host a state banquet for some 170 guests. William and Catherine will join the King and Queen at the top table alongside the President and First Lady, senior ministers, diplomats and military leaders.
The menu, crafted over several days by royal chefs, will showcase British produce while acknowledging American tastes.
The hall will glitter with silver-gilt from the Grand Service, and music from the State Trumpeters of the Household Cavalry will today frame the evening.
While the day’s events are steeped in tradition, their purpose is resolutely contemporary: to reaffirm the enduring defence and trade partnership between the two nations and to signal that, in an unsettled world, the transatlantic alliance remains strong.
That President Trump should become the first American leader to receive two full state visits is, palace officials emphasise, a reflection of the relationship between nations.
For William and Catherine the day will be both duty and debut: a chance to demonstrate that they are ready to shoulder the ceremonial and diplomatic responsibilities that will one day be theirs alone.
