Queen Elizabeth II, 96, appointed the 15th prime minister of her reign, Liz Truss, at her Balmoral home on September 6
Queen Elizabeth II pictured here at Balmoral Castle two days before her death on Sept. 8, 2022, to appoint Liz Truss as prime minister.

New details have emerged regarding the final moments of Queen Elizabeth II's life in a new book about King Charles III called "The Making of a King: King Charles III and the Modern Monarchy", which arrives on Thursday, Jan. 18.

The book by Robert Hardman revealed the preparations Her Majesty made as she was aware that her time on earth was coming to an end. In excerpts of the tome provided by the Daily Mail, the royal author describes how in the aftermath of her death, staff discovered two private letters she had written and left in her red box.

One was addressed to her eldest son King Charles III and the other to her devoted private secretary Sir Edward Young. The author acknowledges that the contents of those letters will unlikely ever be made public. Likewise, the box contained the Queen's final piece of paperwork and last royal order.

"It was the long-list of candidates to fill vacancies in the ranks of the Order of Merit, together with notes on each one, so that the Queen could approve her own shortlist. The OM had always been in the gift of the monarch, not the Government, with membership limited to 24 at any one time. And the Queen had always taken this duty extremely seriously," Hardman writes.

He adds of Queen Elizabeth II's unparalleled devotion to her royal duty even in the final moments before her death: "The paperwork had gone up to her two days before so that she could go through the notes and tick her choices.

"And here it was, completed and returned for Sir Edward to make the necessary arrangements for six new members of the Order of Merit, including the Canadian historian Prof Margaret Macmillan, the author and broadcaster Baroness (Floella) Benjamin, and the geneticist Sir Paul Nurse. It was the last document ever handled by Queen Elizabeth II. Even on her deathbed, there had been work to do. And she had done it."

Elsewhere in the book, Hardman also talks about Queen Elizabeth II's decision to remain in Balmoral even though she was due to be back in London to preside over the resignation of former prime minister Boris Johnson and welcome his successor, Liz Truss.

However, one senior official said that she had asked to remain in Scotland instead. Sir Young then "discussed the matter with the Royal Medical Household and the Cabinet Secretary, Simon Case, who in turn consulted the Prime Minister". They all agreed that the politicians would travel to Balmoral and "the action would all happen in the space of an hour at around lunchtime".

Thus, two days before her death on Sept. 8, 2022, the public saw photos of a beaming Queen Elizabeth II as she waved farewell to Johnson and appointed Truss.

Johnson said later of his meeting with the Queen: "Given how ill she obviously was, how amazing it was that she be so bright and focused."

Likewise, Truss said: "She was clearly physically not very well but we talked for about 20 minutes. She was alert. I would say she was relieved that the thing had actually happened and that we were now moving things forward."

Hardman writes: "Back at Balmoral, staff recall that the Queen had seemed energized after the day's events, all the more so given that 'Love Affairs' had triumphed at Goodwood...But then she said she was going upstairs and would have dinner alone. It was the last time most of her immediate household would see her."

Hardman also shares a memo about Queen Elizabeth II's death from Sir Young, who was at Balmoral when she died. "Very peaceful. In her sleep. Slipped away. Old age...She wouldn't have been aware of anything. No pain," Young notes in the previously unseen memo that is now part of the Royal Archives.