The King will be accompanied by his two sons as he walks behind the Queen’s coffin from Buckingham Palace.
The King, the Prince of Wales and the Duke of Sussex will follow the coffin on foot as it makes its journey to Westminster Hall for lying in state from Wednesday afternoon.
The Duke of York, the Princess Royal and the Earl of Wessex will also be walking with them.
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Princess Anne’s son Peter Phillips and her husband, Rear-Admiral Sir Timothy Laurence, will also join the procession, as will the Duke of Gloucester and the Earl of Snowdon.
The Queen Consort, Princess of Wales, Countess of Wessex and Duchess of Sussex will travel by car.
The procession will leave the palace at 2.22pm and is expected to arrive at Westminster Hall at 3pm.
A service lasting approximately 20 minutes will be conducted by the Archbishop of Canterbury accompanied by the Dean of Westminster.
The brothers’ troubled relationship is well-documented, but following the death of their grandmother last Thursday, they and their wives were unexpectedly united when they saw floral tributes left for the Queen outside Windsor Castle.
The princes joined a united front with their wives during a mammoth outing on Saturday.
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The King spoke of his love for the Duke and Duchess of Sussex in his televised address to the nation on Friday night, saying: “I also want to express my love for Harry and Meghan as they continue to build their lives abroad”.
In the Duke’s tribute to his grandmother, released on Monday, he said he wanted to honor his father at the start of his reign.
The last time Charles and his two sons were together in public was at the service of thanksgiving for the Queen at St Paul’s Cathedral during the Platinum Jubilee celebrations in June.
On that occasion, the Sussexes sat down some distance from Prince Charles and Prince Williambehind the Wessex family and the Duke and Duchess of Gloucester.
This was Harry and Meghan’s first public appearance alongside the Windsors since stepping down as senior royals in 2020.
In April 2021, Harry and William joined their father when they walked behind the Duke of Edinburgh’s coffin at his funeral.
The brothers were separated by Mr. Phillips, their cousin, but he fell back half a step at one point, so the brothers appeared closer.
After the funeral, William and Harry chatted as they walked up the hill from the chapel to the castle.
Mourners are already queuing to attend the Queen’s lie-in-state at Westminster Hall, which begins at 5pm on Wednesday.
It will continue until 6.30am on Monday, the day of the Queen’s funeral.
The government has warned that queues are expected to be very long, with people standing for “many hours, possibly overnight” and with very little opportunity to sit down.