Queen Elizabeth II's grandchildren, including Princes Harry and William, hold vigil at coffin
Prince Harry and Prince William both wore military uniforms for vigil beside Queen Elizabeth II's coffin
{{#rendered}} {{/rendered}}Prince Harry and Prince William joined the rest of Queen Elizabeth II's grandchildren to stand vigil at the queen's coffin on Saturday.
Prince William, who is heir to the throne, stood at the head of the coffin, while Harry was at the foot.
Harry, the duke of Sussex, wore a Blues and Royals No. 1 Uniform, KCVO Neck Order and Star, Afghanistan Operational Service Medal, Golden, Diamond and Platinum Jubilee medals and Army Pilot Wings.
{{#rendered}} {{/rendered}}Also in attendance were Princess Anne's children, Zara Tindall and Peter Philips; Prince Andrew's daughters, Princess Beatrice and Princess Eugenie; and the children of Prince Edward, Lady Louise Windsor and Viscount Severn.
LIVE UPDATES: QUEEN ELIZABETH II LYING IN STATE, PRINCE WILLIAM, PRINCE HARRY HOLD VIGIL
Princess Anne's children, Zara Tindall and Peter Philips; Prince Andrew's daughters, Princess Beatrice and Princess Eugenie; and the children of Prince Edward, Lady Louise Windsor and Viscount Severn attended the queen's vigil. (AARON CHOWN/POOL/AFP via Getty Images)
{{#rendered}} {{/rendered}}Kensington Palace announced the surprise vigil on Friday, and noted Prince Harry would be wearing his military uniform along with Prince William.
Prince Harry and Prince William joined the rest of Queen Elizabeth II's grandchildren to stand vigil at the queen's coffin on Saturday. (Getty Images)
Prince William has been outspoken about the memories that Queen Elizabeth's death brings up for him. The prince of Wales and duke of Sussex's mother Princess Diana died in 1997.
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{{#rendered}} {{/rendered}}William specifically noted the walk behind Queen Elizabeth II's coffin on Wednesday was "challenging" for him.
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"Doing the walk yesterday was challenging," William told the well-wishers in video captured by Sky News. "It brought back a few memories. It's one of those moments where you kind of 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."
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King Charles III, Anne, Princess Royal, Prince Andrew, Duke of York and Edward, Earl of Wessex hold a vigil beside the coffin of their mother, Queen Elizabeth II, as it lies in state on the catafalque in Westminster Hall. (Yui Mok - WPA Pool/Getty Images)
The grandchildren's vigil at Queen Elizabeth II's coffin came one day after King Charles III, Princess Anne, Prince Andrew and Prince Edward stood vigil together.
Queen Elizabeth II will continue to lie in state at Westminster Hall until the early morning hours of Monday, Sept. 19 – the day of her majesty's funeral.
{{#rendered}} {{/rendered}}London police said the funeral will be the largest single policing event the force has ever handled, surpassing even the 2012 Summer Olympics and the queen's Platinum Jubilee in June celebrating her 70 years on the throne.
"The range of officers, police staff and all those supporting the operation is truly immense," said Metropolitan Police Deputy Assistant Commissioner Stuart Cundyhe.
The coffin of Queen Elizabeth II is carried into Westminster Hall for the lying in State. (Dan Kitwood/Pool via AP)
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{{#rendered}} {{/rendered}}Two minutes of silence will be observed Monday across the United Kingdom at the end of Queen Elizabeth II’s funeral, giving British public across the nation a chance to pay their respects to the late monarch.
The Associated Press contributed to this report.