There has been a longstanding tradition in British history of secrecy surrounding the monarch’s health. It’s one of the reasons why Buckingham Palace’s announcement that King Charles III has been diagnosed with cancer on Monday was met with such shock. The unprecedented missive was sparse on details: Charles, 75, had begun treatment for a cancer it did not name after being diagnosed during a recent corrective procedure for an enlarged prostate. The king is stepping back from public duties but carrying on state business during his treatment, which he’ll receive as an outpatient, the palace adde…