Royal reporter Robert Jobson disclosed details in his book, “Catherine, the Princess of Wales: A Biography of the Future Queen,” that Elizabeth II felt “terribly frail” owing to a battle with a type of bone marrow cancer known as myeloma.

“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,” Johnson wrote of his last meeting with the Queen at Balmoral on September 6 when he formally tendered his resignation.

Boris Johnson's decision to reveal the late monarch's diagnosis is likely to raise eyebrows at Buckingham Palace.

Britons are eagerly awaiting the release of former Prime Minister Boris Johnson's autobiography. The politician has included an extensive section about Queen Elizabeth's illness, which he says she struggled with in the final years of her life.