The Queen’s grandchildren will stand vigil beside her coffin in Westminster Hall on Saturday evening.
They will stand around their grandmother for 15 minutes as a mark of respect, Kensington Palace has said.
The Prince of Wales will stand at the head and the Duke of Sussex at the foot. They will both be in uniform at the King’s request.
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Harry has been denied the chance to wear his military uniform as he publicly mourns because he is no longer a working royal – despite seeing action on the front line during two tours of duty in Afghanistan.
Their spouses will not attend the vigil.
The Queen’s other grandchildren will be in morning suits and dark formal dresses with decorations.
William will be flanked by his cousins, Zara Tindall and Peter Philips, the children of the Princess Royal.
Harry will be with the Duke of York’s daughters, Princesses Beatrice and Eugenie.
The Earl of Wessex’s children, Lady Louise and Viscount Severn, will stand near the middle of their grandmother’s coffin.
The grandchildren will pay their respects on Saturday after their parents have done the same on Friday evening.
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It comes after the Prince of Wales spoke about the ordeal of taking part in the procession as the Queen left Buckingham Palace for the last time.
Prince William told a member of the public it “brought back a few memories”. The royal famously walked behind his mother Diana’s coffin in 1997.
Speaking to mourners at Sandringham, the future monarch added: “It’s one of these moments where you kinda think to yourself I’ve prepared myself for this but I’m not that prepared.
“It’s this weird kind of thing… because we knew she was 96”.
Prince William and Kate held hands as they viewed the tributes people had left to his grandmother.
They went on to chat and shake hands with some of those who had turned out to honour the late monarch.
Meanwhile, Prince Edward and his wife Sophie, the Countess of Wessex, travelled to Manchester to meet people at St Ann’s Square. They shook hands and spoke to members of the public, with the Countess of Wessex leaning over the barrier to hug a child.
“Thank you very much indeed, thank you everybody,” Prince Edward said before leaving to a round of applause.