Queen Elizabeth II died on Sept. 8, 2022, and a death certificate showed the cause of death is old age. But author Gyles Brandreth claimed she secretly battled bone cancer in her final years.

Prior to her passing at the age of 96, Her Majesty suffered from mobility issues which prompted her to limit her royal duties to desk work and in-office meetings. Her final engagement was with the then-U.K. Prime Minister Liz Truss at Balmoral Castle on Sept. 6. Buckingham Palace also shared what would be the Queen's final photo which had the public worried since it showed her with what they believe was a purple bruise on her hand.

In the months leading up to her death, there were speculations that she was dealing with an illness. Brandreth wrote in his book "Elizabeth: An Intimate Portrait," which will be serialised by the Daily Mail, "I had heard that the Queen had a form of myeloma — bone marrow cancer — which would explain her tiredness and weight loss and those 'mobility issues' we were often told about during the last year or so of her life."

He continued, "The most common symptom of myeloma is bone pain, especially in the pelvis and lower back, and multiple myeloma is a disease that often affects the elderly."

Brandreth added, "Currently, there is no known cure, but treatment — including medicines to help regulate the immune system and drugs that help prevent the weakening of the bones — can reduce the severity of its symptoms and extend the patient's survival by months or two to three years."

The author wrote that Her Majesty suffered a sudden drop in energy by autumn last year and she was advised by her doctors to take it easy. She reportedly agreed albeit reluctantly and said, "I've got to be sensible."

In the latter months of her life, Brandreth wrote that Queen Elizabeth II's health rapidly deteriorated. But she "always knew that her remaining time was limited" and accepted her health woes with "good grace."

Buckingham Palace has yet to respond to rumours that Queen Elizabeth II suffered from bone cancer before her death. As for Brandreth, his book on the queen will come out on Dec. 8, 2022.

Queen Elizabeth II's death aged 96 triggered more than a week of national mourning
Queen Elizabeth II's death aged 96 on Sept. 8, 2022 triggered more than a week of national mourning AFP News