Princes William and Harry will walk behind the queen’s coffin on Wednesday as the cortege makes its way to Westminster Hall, in echoes of the funeral of their mother, Princess Diana, 25 years ago.
The two princes will join King Charles III, Prince Andrew, Princess Anne and Prince Edward, following the coffin on foot as it makes its way to Westminster.
Princess Anne’s son Peter Phillips and her husband, Vice Adm Sir Tim Laurence, will also walk in the procession, as well as Prince Richard, the Duke of Gloucester, and David Armstrong-Jones, the Earl of Snowdon.
Queen Consort Camilla, Catherine, the Princess of Wales, Sophie, the Countess of Wessex, and Meghan, the Duchess of Sussex, will travel by car.
The sombre walk will no doubt stir memories for the princes of the funeral of Princess Diana, when the brothers joined Prince Philip, Earl Spencer and Prince Charles, as he was at the time, to lead the procession.
The duke of Sussex spoke about the lasting impact the walk had on him in a documentary series on mental health released last year.
He was only 12 when he joined the walk, "sharing his grief with the world".
Prince Harry said: “For me, the thing I remember the most was the sound of the horses' hooves going along the pavement. Along The Mall, the red brick road. By this point I was, both of us were, in shock.”
He said he was doing “what was expected of me” even though he was experiencing profound grief.
“It was like I was outside of my body,” he said.
“Showing one 10th of the emotion that everybody else was showing. I thought, ‘This is my mum. You never even met her’.”
Wednesday’s procession will leave the palace at 2.22pm, making its way along The Mall, Horse Guards Road, across Horse Guards Parade and on to Whitehall to Parliament Square and into the Palace of Westminster, arriving about 3pm.
A service lasting about 20 minutes will be led by the Archbishop of Canterbury, Justin Welby, accompanied by David Hoyle, the Dean of Westminster.
The doors to Westminster Hall will then be opened, allowing the public to file past to pay their respects to the queen from 5pm.
The hall will be open round the clock until early on Monday, the morning of the queen’s funeral.
Organisers expect thousands to attend to pay their respects, and have prepared for queues of up to eight kilometres in length.
They are warning people to prepare for a long and physically demanding wait, with few opportunities to sit down.
Everyone arriving at the hall will be issued with wristbands, which will allow them to pop out for a short time for food or drink.
The queen's coffin will be guarded round the clock until the funeral by members of the Household Division or Yeoman Warders of the Tower of London, who are the sovereign's bodyguards.