King Francis I of France (reigned 1515–1547) suffered from several chronic conditions, most notably syphilis, which he likely contracted during his Italian campaigns. This led to persistent abscesses and declining health in his later years. However, if you are referring to his grandson, King Francis II (husband of Mary, Queen of Scots), he suffered from a severe and ultimately fatal ear infection (otitis media). In late 1560, the infection progressed into a cerebral abscess or meningitis. Contemporary accounts describe intense pain and swelling behind the ear, likely mastoiditis, which modern medicine could have easily treated with antibiotics. Without them, the infection spread to his brain, leading to his death at just 16 years old. His short reign of only 17 months was defined by this frailty, leaving a power vacuum that his mother, Catherine de' Medici, eventually filled as regent for his younger brother.