The secret to the longevity of their relationship is a mixture of national duty, commitment and a dollop of love thick enough to spread out across the decades. Their common bond is that neither has a life of their own: her role is to serve the nation and his is to support her.
The couple returned to Westminster Abbey yesterday for a service to celebrate their 60th wedding anniversary, at which Dr Rowan Williams, the Archbishop of Canterbury, said: "Some couples have to live more than others in the full light of publicity."
It was a sentiment Andrew Motion, the poet laureate, shared. A line from his latest poem, Diamond Wedding, reads: "A life remote from ours because it asked each day, each action to be kept in view."
For the Queen, her husband has been, to quote another royal, her "rock". On the occasion of their golden wedding anniversary, she said: "He has, quite simply, been my strength and stay all these years and I, and his whole family, and this and many other countries, owe him a debt greater than he would ever claim or we shall ever know."
Lord Charteris, a friend of the couple, told Gyles Brandreth, the author of Philip and Elizabeth: Portrait of a Marriage, that the success of their union was founded on directness. He said: "Prince Philip is the only man in the world who treats the Queen simply as another human being. I think she values that. And, of course, it is not unknown for the Queen to tell the duke to shut up."
This directness was illustrated by the story that when the prince was driving the Queen on one occasion she kept tutting at his speed, to which he replied that if she did it once more he would put her out of the car.
The couple met when Elizabeth was 13 and paid a visit to the Royal Naval College, where Philip was the 19-year-old cadet captain who led her tour. They began "dating" a few years later and their wedding, on 20 November, 1947 was a colourful highlight for a nation beaten down by war. Their wedding gifts included a horse, 131 pairs of nylon stockings - a luxury during rationing - and 500 tins of pineapple. Mahatma Gandhi sent a hand-spun lace tray cover, which Queen Mary, Princess Elizabeth's grandmother, mistook for his loincloth.
Prince Philip was the "Fergie" of his day, deemed unsuitable by the Establishment. Although the great-great-grandson of Queen Victoria, and the son of Prince Andrew of Greece, Philip was considered from poor stock. His father was a playboy, while his mother, Princess Alice, was committed to a lunatic asylum when her son was eight.
There were fears about his potential for fidelity. Sir Alan Lascelles, private secretary to George VI, was quoted as saying: "They felt he was rough, uneducated and probably would not be faithful."
Yet all was forgiven when Princess Elizabeth fell pregnant within three months with a male heir. It may seem unseemly to try to peer into the monarch's bedchamber but, as a brace of royal authors have reported, the couple were clearly infatuated. When they visited friends in their early years, it was noted that while playing party games, they found one another quite easily in the dark.
Like many upper-class members of their generation, each had their own bedroom, a practice they have retained. The Queen, however, has had to deal in her own way with the firm friendships that Prince Philip has had with women over the years. The extent of such friendships is unknown. In Elizabeth, her biography of the Queen, Sarah Bradford described Philip's fidelity as something courtiers will "defend to the death", while Brandreth insists the prince has never strayed. When Prince Philip was asked about the secret to his marriage he replied: "The Queen has the quality of tolerance in abundance."
The Queen is aware of the sacrifices her husband made as he had to give up a promising naval career, which he adored. The Queen may be head of state, but Philip is clearly head of the family. It was he who persuaded her that Charles should marry Camilla Parker Bowles, while he supported the Queen during the traumatic week of Diana's death, when the nation appeared to move against her.
Robert Lacey, the author of Royal: Her Majesty Queen Elizabeth II, said the key ingredient to their marriage was separateness: "He was offered the opportunity to be a prince consort that would have allowed him access to Queen's state papers and he didn't want it.
"He wanted to carve out his own roles, which he has done. Within the marriage, he is master of the house. He is his own man and the Queen loves him for it. His jokes, or gaffes as they are called, the Queen quite enjoys."
The marriage, the longest and most successful of any British monarch, was captured best by Lady Penn, a friend of the Queen and a former lady-in-waiting to the Queen Mother. She said: "They are good friends and that is their secret. She has had a lot to contend with. The fact she has coped so wonderfully is mostly thanks to him."
OTHER DIAMOND COUPLES SHARE SPECIAL DAY
THE Queen yesterday shared her "very special" milestone with other diamond wedding anniversary couples who married on the same day. Eight husband-and-wife pairs from across the UK had a surprise meeting with the Queen and the Duke of Edinburgh at the end of their celebratory service at Westminster Abbey.
Just like Princess Elizabeth and Lt Philip Mountbatten 60 years ago, the couples also married on Thursday, 20 November, 1947.
Peter and Joyce Philip, from Ripon, North Yorkshire, were among those who congratulated the royal couple. Mrs Philip, 86, revealed the Queen spoke of how it was a "very special day". "She said, ' It's a very special day and thank you for being here'. She asked where we were married. It's wonderful to be here, it's a great achievement."
Mr Philip, 85, said: "It makes it easy to remember your anniversary. I feel lucky to be here."
Sidney Royle, from Knutsford, Cheshire, was accompanied by his wife Margery. Mr Royle, 81, said: "She's so pleased to be here. It was tremendous. I have married the best woman in the world. She had no sleep because she was so tremendously excited."