Former United Kingdom Prime Minister Boris Johnson is revealing alleged private information about the death of Queen Elizabeth II. 

Her Majesty, who passed away in September 2022, was battling "a form of bone cancer," according to Johnson, and had known by the summer "she was going." 

Official documents released after the queen's death confirmed the cause as old age. She was 96.

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Queen Elizabeth II smiles in a teal jacket and matching hat with feathers sticking out

According to former United Kingdom Prime Minister Boris Johnson, Queen Elizabeth II had "a form of bone cancer" in the last years of her life. (Jane Barlow - WPA Pool/Getty Images)

Johnson wrote about this in his forthcoming book, "Unleashed," where he recounts his final interactions with the queen. In an excerpt obtained by the Daily Mail, Johnson wrote that he visited the queen at her Balmoral residence just two days before the U.K.'s longest reigning monarch died. Earlier that summer, Johnson had resigned from Parliament.

"Like all my 13 predecessors, I had come to spend the last hour of my premiership in the company of Queen Elizabeth II. The date was September 6, 2022, more than two months after I had resigned as prime minister, and under our ­system I had been required to stay on and mind the shop while the Conservative Party got on with choosing a new leader.

"It had been a rather frustrating summer," he wrote. 

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Boris Johnson in a suit and bright blue tie shakes hands with Equerry Lieutenant Colonel Tom White and her private Secretary Sir Edward Young ahead of his visit with the Queen

Prime Minister Boris Johnson, right, shakes hands with the queen's private secretary, Sir Edward Young, ahead of his meeting with Her Majesty at Balmoral. (ANDREW MILLIGAN/POOL/AFP via Getty Images)

Once at Balmoral with his wife, Carrie, Johnson could sense lingering fatigue among the staff. 

"Edward Young, her private secretary, tried to prepare me," Johnson wrote, according to the outlet. "I had known for a year or more that she had a form of bone cancer, and her doctors were worried that at any time she could enter a sharp decline."

Rumors that the queen battled myeloma, a bone marrow cancer, during the last years of her life have never been confirmed, although reported.

When reached for comment by Fox News Digital, Buckingham Palace said, "We will not be offering guidance or comments on this, and this should not be seen as guidance of fact."

Johnson wrote that Young told him the queen had "gone down quite a bit over the summer." When they met, Johnson wrote, "she seemed pale and more stooped, and she had dark ­bruising on her hands and wrists, probably from drips or injections."

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A frail Queen Elizabeth in a plaid skirt and light grey sweater smiles while holding a cane and wearing glasses

Queen Elizabeth II is photographed at Balmoral Castle two days prior to her death. (JANE BARLOW/POOL/AFP via Getty Images)

"But her mind – as Edward had also said – was completely ­unimpaired by her illness, and from time to time in our ­conversation she still flashed that great white smile in its sudden mood-lifting beauty."

Johnson wrote of his close relationship with the queen, admitting "there was nothing I could not tell her." He remembered lamenting about the COVID-19 pandemic, how it had impacted individuals and also the economy.

"'Oh well,'" Johnson remembers the queen saying. "'I suppose we will all just have to start again.'"

Boris Johnson in a black suit greets Queen Elizabeth in a very pale blue dress at Buckingham Palace

Boris Johnson detailed his close relationship with Queen Elizabeth, photographed here in 2021 at Buckingham Palace. (DOMINIC LIPINSKI/POOL/AFP via Getty Images)

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"I realized that she spoke with the historical knowledge of someone who had actually served in uniform in the Second World War, and whose first PM was Winston Churchill. She knew her kingdom was infinitely capable of rebounding and recovering. We just needed to get a grip, and get on with it," Johnson wrote, according to Daily Mail.

Johnson said that the queen's secretary later explained to him, "she had known all ­summer that she was going, but was determined to hang on and do her last duty: to oversee the peaceful and orderly transition from one government to the next – and, I expect, to add another departing PM to her record-breaking tally."

Queen Elizabeth smiles and looks off in the distance in a blue patterned dress and strings of pearls at Windsor Castle

Boris Johnson said that while the queen's health declined, her mind did not deteriorate. (Dominic Lipinski - WPA Pool/Getty Images)