The Queen's eight grandchildren will stand side by side at her vigil - with Prince Harry in his military uniform.
The service will see the royals - led by Prince William - perform the guard ceremony around Her Majesty's coffin tomorrow evening at Westminster Hall.
It comes after The Mirror revealed yesterday that despite the Duke of Sussex no longer being a working royal, he has been given special permission to wear his colours by dad King Charles.
A statement from Buckingham Palace this morning confirmed the Prince of Wales will "stand at the Head" with his younger brother "at the Foot".
It adds: "At the King’s request, they will both be in uniform. The other grandchildren will be in Morning Coat and Dark Formal Dress with Decorations."
During an initial vigil tonight for the late monarch's children, Prince Andrew - who was forced to quit his active role in the Firm - will also be wearing his uniform.
The two dukes were seen with their medals pinned to morning suits during the procession from Buckingham Palace on Wednesday.
Palace officials are understood to have intervened after Andrew was given the initial green light to ensure Harry was afforded the same privilege.
A royal source said: “Common sense has prevailed.
“It was a ludicrous situation given the Duke of Sussex has served his country and is a highly respected member of the armed forces with everything he has done for veterans.
"It is important that the Queen's grandchildren are all made to feel welcome and comfortable as they grieve their beloved grandmother together."
The Queen's other grandchildren, including Princesses Beatrice and Eugenie, Zara and Peter Philips and Lady Louise and James, Viscount Severn, are also understood to form part of the guard of honour tomorrow evening.
Today's Palace statement goes on to say: "The Prince of Wales will be flanked by Mrs Zara Tindall and Mr Peter Philips; The Duke of Sussex by Princesses Beatrice and Eugenie, with Lady Louise and Viscount Severn at the middle of the coffin.
"The grandchildren, at the King’s invitation, are very keen to pay their respects – just as their parents are doing the evening before."
Harry, who served in the British army for a decade including two tours of Afghanistan, had this week been at the centre of a row over whether he would be allowed to wear his Blues and Royals uniform.
After quitting his royal role in 2020 he was unceremoniously stripped of his cherished military appointments and banned from wearing his military uniforms in public.
On Tuesday, Prince Harry, who served two front line tours of duty in Afghanistan, addressed the rule barring him from wearing his military uniform in a statement released through his spokesperson.
He confirmed he would be wearing a morning suit and asked that the “focus remain on the life and legacy of Her Majesty Queen Elizabeth II”.
The Queen's funeral is expected to see the Abbey filled with over 2,000 guests on Monday morning.
The cortege will then leave London for Windsor and a committal service will take place at St George’s Chapel Windsor Castle at 4pm.
Some 800 people, including members of the Queen’s Household and Windsor estate staff, will attend the committal service.
The Queen will later be buried with the Duke of Edinburgh in King George VI’s chapel in Windsor Castle in a private service at 7.30pm the same day.
The burial service conducted by the Dean of Windsor and attended by the King and royals will remain entirely private, as a “deeply personal family occasion”.
* You can now buy last Friday's historic Daily Mirror commemorating the death of the Queen here: mirror.co.uk/commemorative
