Anyone wishing to understand the machinery that drives Queen Elizabeth II should turn to its designer — her redoubtable grandmother, Queen Mary. The consort of King-Emperor George V, Queen Mary came from peripheral royal stock. Her mother, the portly Princess Mary Adelaide, although a first cousin of Queen Victoria, had difficulty finding a husband. Eventually, at the age of 30, she married an impecunious German prince, Francis of Teck. Habitually short of funds, she appealed to Queen Victoria for handouts, which were usually denied.

Queen Victoria, though, despite the insularity of her royal existence, remained a shrewd judge of character. She selected her poor cousin’s daughter May (later renamed Mary) to be the wife of her grandson, Prince Albert Victor. He died prematurely in 1892 (the year after he visited Lahore). Not to be thwarted, Queen Victoria arranged for his younger brother, George, to marry May. Over time, Princess May (later Queen Mary) consciously perfected the image of monarchy. She dressed the part, carrying a queen’s ransom of jewellery on her ample person. She restored the palaces and she pursued and recovered furniture and paintings from the royal collection that had been dispersed.

Above all, she gave the monarchy a singular glittering pre-eminence, like the golden apex that once adorned the pyramids at Giza. From 1936, when Queen Mary knew that her eldest son Edward’s decision to abdicate was irreversible, she applied her prodigious energies to support her second son, now King-Emperor George VI. Of paramount importance to her was the continuity of the monarchy. To this end, she commenced a rigorous programme of training for her granddaughter, Elizabeth, to become the next queen regnant. She organised tutorials in British history, in its constitution, heraldry, and royal traditions. She took her to stately homes, museums and art galleries. She made her an expert in royal etiquette. She died in 1953, before Queen Elizabeth II could be crowned.

In the last year of her life, though, she imparted her knowledge and unique experience of three coronations — that of her in-laws in 1902, her own in 1911, and her son’s in 1937. And to dress her for the role, she bequeathed her treasure trove of jewellery to the young queen. Today, after 70 years on the throne, Queen Elizabeth is herself a matriarch, a great-grandmother. Like Queen Victoria and Queen Mary, she has been photographed as the centrepiece of a tableau displaying four generations of British monarchy. It is the same reverence for the institution of monarchy that has sustained Queen Eliza-beth II throughout her 70-year-long reign — the longest in the UK since Queen Victoria’s.

She is the second longest reigning monarch in history after the French King Louis XIV, who reigned for 72 years. But then, he ascended the throne at the age of four and began his personal rule only 19 years later. Queen Elizabeth II has lived through the turbulence of her uncle’s abdication; the Second World War; the dissolution of the British Empire; the fractured marriages of her sister Margaret and three of her own children; the anti-monarchist wave that followed the death of Diana, Princess of Wales; Brexit; the sexploits of Prince Andrew, and now the betrayal by Prince Harry. She has outlived her critics — Lord Altrin-cham, who derided her style of speaking as “a pain in the neck”, and the playwright John Osborne, who described the monarchy as “a gold filling in a mouth of cavities”.

She has met countless world leaders, including revisionist Russians and communist Chinese, and every US president (bar one, Lyndon B. Johnson) since Dwi-ght D. Eisenhower. Sportingly, she played her part in a James Bond spoof for the Olympic Games 2012 and had tea and a marmalade sandwich with Paddington the Bear to mark her Platinum Jubilee festivities. She will never, though, make a guest appearance on the television series The Crown. Having performed her duty, she is training the Duchess of Cornwall and the Duchess of Cambridge to perpetuate the monarchy.

Although 96 years old and frail, she will never abdicate. Forced into incapacity, she might appoint Prince Charles as Regent, but she is determined to reign as long as she can. She has the example of her grandmother Queen Mary before her. In her final years, the ailing Mary mused to Lady Shaftesbury: “I suppose one must force oneself to go on until the end.” The deferential reply was also a cruel reminder that a queen is wedded for life to the crown: “I am sure that Your Majesty will.”