The seventh episode of The Crown season 4 is titled "The Hereditary Principle," which on first glance seems to be a reference to Princess Margaret's (Helena Bonham Carter) discovery of her
long-hidden cousins, Nerissa and Katherine Bowes-Lyon. The cousins were born with severe developmental problems and spent their adult lives in a psychiatric ward. Margaret, who has been struggling with her own mental health, fears that she may be doomed to the same fate thanks to genetics.
But in fact, the Hereditary Principle refers to the system that governs the British monarchy and its line of succession. In a hereditary monarchy, the transfer of power is governed by bloodlines. Per BBC History magazine, "power and titles pass from family member to family member." And in the episode, Princess Margaret's place within the hereditary hierarchy is diminished when Queen Elizabeth's youngest son, Edward, comes of age. Below, a primer on exactly what happened here.
Where is Princess Margaret in the line of succession?
The royal line of succession runs in birth order, meaning that at the time of King George VI's death in 1952, Elizabeth was first in line to the throne and Margaret was second. Elizabeth and Prince Philip's four children, Charles, Andrew, Edward, and Anne, were all born ahead of Margaret in the line of succession. Anne is behind her brothers—and their children—because of a sexist tradition that was finally changed in 2013. By 1985, when the episode takes place, Margaret was ninth in line, behind the queen's four children and four grandchildren (Charles and Anne each had two children at this point).
How did Prince Edward's birthday in 1985 impact Princess Margaret's position in the monarchy?
This is where the 1937 Regency Act comes in. As the queen's private secretary Martin Charteris explains in the episode, the act created a list of senior royals who could be called on to deputize for the monarch in an official capacity; these royals are called Counsellors of State. Now that Edward has turned 21, he is considered to be of age (later versions of the Act amended this to 18), which doesn't change his place in the line of succession, but does mean he'll automatically be added to the Regency Act list—in place of Margaret. The Regency Act restricts the number of Counsellors of State to just six, per BBC History, and Margaret no longer makes the cut; the six who did were Prince Philip, the Queen Mother, Prince Charles, Prince Andrew, Prince Edward, and Princess Anne.
The Act reads: “An Act to provide that, in the event of a Regency becoming necessary under the Regency Act 1937, His Royal Highness the Duke of Edinburgh shall in certain circumstances be the Regent, to provide that the heir apparent or heir presumptive to the Throne shall be deemed for the purposes of that Act to be of full age if he or she has attained the age of eighteen years, to add Her Majesty Queen Elizabeth the Queen Mother to the persons to whom royal functions may be delegated as Counsellors of State, and for purposes connected with the matters aforesaid.”
Margaret, therefore, is asked to relinquish her role as counsellor of state. The episode really sticks the knife in here, because just days earlier, Margaret has all but begged the wueen to give her more responsibility, not less. "I’m finally ready to focus on the one thing that won’t let me down," she says, in an uncharacteristic moment of vulnerability after a romantic rejection. "Us. My position as a royal. My duty. I come on bended knee with a familiar request: Give me as much responsibility as you can. What your sister needs to stay afloat is a sense of meaning."
The queen gives her a pained smile before breaking the news days later. In real life, there isn't much reporting around how Margaret reacted to the demotion.
Margaret's ill health also played a role in her stepping back from royal duties.
As depicted in the episode, Margaret underwent a serious lung operation at London's National Heart and Chest Hospital in January of 1985. During the surgery, she had part of one of her lungs removed, which was found not to be cancerous.
“Princess Margaret underwent an operation yesterday,” the hospital said in a statement, per AP. "This was to remove a small area of her left lung, which was found to be innocent.” But the cancer scare was particularly worrying given Margaret's family history. Her father, King George VI, died of lung cancer, and she had been a heavy smoker throughout her life.
According to BBC History, Margaret's failing health led to her being seen more positively by the press and the public. "News editors were aware of her personal situation, so treated her more sympathetically," the magazine quotes royal historian Dr. Ed Owens as saying. “As the public’s attention shifted to the activities (and antics) of Princess Diana and Sarah Ferguson, Margaret was gradually regarded with greater affection. She disapproved of the behavior of the younger royal women, and she re-asserted herself in public life as a figure who was devoted to her duty and the queen, playing the role of reliable sister and confidante.”