A new book has claimed that the Queen was battling cancer in the last few months of her life before she died.

The official cause of death for Queen Elizabeth II was listed as "Old age" when she passed away in September at the age of 96.

However, Gyles Brandreth, a friend of Prince Philip, has claimed differently in an upcoming biography called Elizabeth: An Intimate Portrait, as reported by The Mirror.

The broadcaster and former politician has said that the monarch was battling a rare form of bone marrow cancer.

Richmond and Twickenham Times: Queen Elizabeth's official cause of death was listed as old ageQueen Elizabeth's official cause of death was listed as old age (Image: PA)

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.

READ MORE: Queen Elizabeth II's cause of death revealed as death certificate released

"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 biographer also claimed that the Queen suffered periods of low energy, despite telling aides that she was determined to stay busy after the death of Prince Philip.