Article continues below advertisementPrince Philip is said to have endured a long, largely hidden battle with pancreatic cancer - with insiders now telling OK! the "brutal" royal tradition of maintaining a stiff upper lip was a key reason his illness remained secret for years.Philip, who died in April 2021 at age 99, was diagnosed with cancer in 2013 and lived with the disease for eight years, according to new details revealed by royal biographer Hugo Vickers in his book Queen Elizabeth II: A Personal History.