<p>King Charles III has been diagnosed with cancer. This is an unexpected announcement: it is unusual for the royal family to release details of medical conditions to the public.</p> <p>"Don't let the daylight in" was how British essayist Walter Bagehot advised the British monarchy to deal with the public in 1867. "[A]bove all things our royalty is to be reverenced […] its mystery is its life," he wrote.</p> <p>For Queen Elizabeth II this attitude framed her response to public information about the royals, quipping "never complain, never explain". Maybe this explains why Princess Kate's recent abdominal surgery has not been disclosed to the public, with media reports saying she is "determined to keep her medical details private".</p> <p>In revealing the fragility of the royal body much of the mystique about them as anointed by God fades away. But the royals' health has, occasionally, been the subject of official news, and, more commonly, the subject of gossip.</p>