Mortality looms large in season 4 of The Crown, with Lord Mountbatten assassinated in the first hour of the season, Prince Charles narrowly avoiding death in an avalanche that claims the life of his close friend Hugh Lindsay, and Princess Margaret's health declining to the point where she needs lung surgery. In the show, Margaret's surgery coincides with her forced demotion from royal duties, which only worsens her depression and feeling of hopelessness. And although the surgery is a success, the Queen is visibly concerned about Margaret's declining health. Here's a primer on the true story of her surgery and illness.