Charles, William and Harry – along with Prince Andrew, Princess Anne and Prince Edward – will follow the coffin on foot as it makes its journey to Westminster Hall on Wednesday afternoon.
Anne’s son Peter Phillips and her husband Vice Admiral Sir Tim Laurence will also walk in the procession, as well as the Duke of Gloucester and the Earl of Snowdon.
Camilla, Queen Consort, Kate, Princess of Wales, Sophie, Countess of Wessex and Meghan, 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 around 20 minutes will be led by the Archbishop of Canterbury accompanied by the Dean of Westminster.
William and Harry put on a united front with their wives during a mammoth walkabout on Saturday.
The brothers have a well-documented troubled relationship but the death of their grandmother saw them unexpectedly come together when they viewed floral tributes left to the late Queen at Windsor Castle.
William, Kate, Harry and Meghan arrived in the same vehicle and greeted well-wishers for around 40 minutes before William hopped into the driver’s seat of the Audi with his wife in the passenger seat, and his brother and sister-in-law in the back.
In his televised address to the nation on Friday evening, the King talked of his love for Harry and Meghan, saying: “I want also to express my love for Harry and Meghan as they continue to build their lives overseas.”
Then in Harry’s tribute to his grandmother, released on Monday, Harry said he wanted to honour his father at the start of his reign as King.
The last time Charles and his two sons were all seen together in public was at the service of thanksgiving for the Queen in St Paul’s Cathedral during the Platinum Jubilee celebrations in June.
But on that occasion, Harry and Meghan were seated some distance from Charles and William on the other side of the aisle in the second row, behind the Wessex family and the Duke and Duchess of Gloucester.
This was Harry and Meghan’s first public appearance alongside the Windsors since they stepped down as senior royals in 2020 amid the Megxit storm.
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 their cousin Peter Phillips but he dropped back half a pace at one point so the siblings appeared closer together.
After the funeral service, William and Harry could be seen chatting as they walked back up the hill from the chapel to the castle.
Mourners have already joined the queue to attend the Queen’s lying in state at Westminster Hall which begins at 5pm on Wednesday.
It will continue until 6.30am on September 19 – the day of the Queen’s funeral.
Government guidance says the queue is expected to be very long, with people standing for “many hours, possibly overnight” and with very little opportunity to sit down.
King Charles III, Prince William and Prince Harry Reuters
Queen Elizabeth II's coffin was moved to Buckingham Palace on Tuesday evening Jack Hill