A new book about Queen Elizabeth II claims she was battling cancer during the last year of her life. Although reports say the official cause of death was old age, Gyles Brandreth, author of Elizabeth: An Intimate Portrait, says the monarch was suffering from myeloma, a serious and rare form of cancer.

“I had heard that the Queen had a form of myeloma, also called multiple myeloma, which would explain her tiredness and weight loss and those ‘mobility issues’ we were so often told about during the last year or so of her life,” Brandreth says, according to Eat This, Not That!. “The most common symptom of myeloma is bone pain, especially in the pelvis and lower back, and multiple myeloma is a disease that affects the elderly.”

Brandreth says there is currently no known cure for the disease, but treatment that includes medicines to regulate the immune system and drugs that help prevent weakening of the bones can reduce the severity of symptoms and extend a patient’s survival.

According to the American Cancer Society (ACS) about 34,470 new cases of multiple myeloma will be diagnosed in the United States in 2022, and approximately 12,640 deaths from the rare cancer will occur. Multiple myeloma is a cancer of plasma cells, white blood cells that make antibodies and protect us from infection. The cells grow out of control, crowding out normal cells in the bone marrow.

The disorder is characterized by low blood counts. This can cause anemia and sufferers can become weak and fatigued. Myeloma cells also interfere with cells that help keep bones strong and inhibit the growth of new bone. The ACS says that fractured bones are a major problem in people with myeloma.

People with multiple myeloma often suffer from infections. Normal plasma cells produce antibodies that attack germs. In multiple myeloma, the cancerous cells crowd out the plasma cells, so your body has a harder time fighting infections.

Kidney damage and kidney failure is another sign of multiple myeloma as the myeloma cells make an antibody that can harm the kidneys, says the ACS.

Author Brandreth said that “Her Majesty always knew that her remaining time was limited,” according to Newsweek. “She accepted this with all the grace you’d expect.”