The Queen 'was battling cancer' in the last few months of her life, a new biography has claimed.
Gyles Brandreth, a friend of Prince Philip, made the claims about Her Majesty, 96, in an upcoming biography called Elizabeth: An Intimate Portrait.
Her Majesty's official cause of death was listed as "old age", but Brandreth claimed it was actually a rare form of bone marrow cancer that took the Monarch's life.
Brandreth wrote: "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.
"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.
"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 book, serialised on Mail+, also claims the Queen suffered periods of low energy, despite telling aides she was determined to stay busy after Philip's death in April last year.
When Her Majesty felt weaker she filled her time by by watching BBC drama Line of Duty, the biographer claimed.
My husband would certainly not have approved," she is reported to have said, quashing any attempt at sympathy.
It comes after reports one of the Queen’s final wishes before she passed away has been carried out by King Charles, as six new people are appointed to the UK's distinguished Order of Merit.
The late Queen Elizabeth chose the select six in early September, before she died, Buckingham Palace insisted.
And in his first such duty as Sovereign of the order, King Charles has now ratified his mother's decision.
TV presenter and author Baroness Floella Benjamin is among six people chosen to become members of the Order of Merit.
Among the distinguished group, who are appointed by the King, are a molecular biologist and a geneticist who have received the Noble Prize, an award-winning architect, a former nurse who led sickle cell treatment and a leading historian.
The Order of Merit was created in 1902 by Edward VII to honour leaders in areas of arts, sciences, culture and military.
Appointments are in the Sovereign's personal gift and the six were chosen by the late Queen in early September.