The King and Queen Consort have made their first appearance of coronation day - travelling the short distance from their Clarence House home for final preparations at Buckingham Palace.
Crowds cheered as they caught sight of Charles and Camilla being driven in a state limousine between the royal residences.
They are due to leave the palace at 10.20am local time and travel in a procession to Westminster Abbey where first the King and then the Queen will be anointed and crowned by the Archbishop of Canterbury, Justin Welby.
The Duke of York was also seen being driven down The Mall in a state car, with parts of the crowd booing as he went past.
Celebrity guests have begun arriving at Westminster Abbey for the King's coronation as thousands flocked to the capital to share in the historic day.
Actress Emma Thompson, musicians Lionel Richie, Australian Nick Cave and a cheery-looking Ant and Dec, in their smart morning suits, were photographed entering the place of worship.
Inside the ancient abbey, the church buzzed with noise as the congregation filed in and took their seats hours before the ceremony was due to start.
Crowds had been building up in the capital since dawn with the streets around the procession route - including Trafalgar Square, Whitehall and Parliament Square - thronged with people.
As anticipation mounted among royal fans, a group of republicans were arrested more than four hours before the coronation service began.
The King will be crowned during a coronation ceremony dating back centuries.
Cries of God Save the King will ring out around the abbey after St Edward's Crown is placed on Charles' head by Mr Welby.
The senior cleric said in a statement issued on the eve of the coronation that the ceremony served as "a powerful reflection and celebration of who we are today, in all our wonderful diversity".
He said people will be struck by the "majesty and sacred wonder" of the service, but also hoped they would find "ancient wisdom and new hope".
The event will bring together around 100 heads of state, kings and queens from across the globe, celebrities, everyday heroes and family and friends of the couple, with Charles' estranged son Harry expected to attend.
Invited guests include David and Victoria Beckham, French President Emmanuel Macron, King Willem-Alexander and Queen Maxima of the Netherlands, Prime Minister Rishi Sunak and US First Lady Jill Biden but her husband President Joe Biden will not be attending.
The day will be a display of pomp and pageantry, with the nation's army promising a "spectacular" event when the King and Queen process through the streets of the capital.
The event is the military's largest ceremonial operation since Queen Elizabeth II's 1953 coronation, with 9000 servicemen and women deployed and 7000 of these performing ceremonial and supporting roles.
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