To understand what lies at the heart of William and Kate, the Duke and Duchess of Cambridge's marriage, and how they have managed to escape the Windsor curse, you have to go back to July 29, 1980.
It was a Tuesday and crowds had gathered at Cowdray polo club to watch Prince Charles do his darnedest with his mallet and there among the bevy of Sloane-y gals watching the future king was an intriguing new face.
On the day, The Sun's long-time royal photographer Arthur Edward had heard a whisper that Charles had a new girlfriend but when he spotted the 19-year-old he snapped a few shots but dismissed things. She was so young and a nursery teacher.
The girl was, of course, the teenage Lady Diana Spencer and exactly a year to the day later, she would walk down the aisle of St Paul's in London while a global audience of 750 million people watched on.
Later, she would reveal she felt like a "lamb to the slaughter" on her wedding day but to the outside world, she was a fairytale made flesh and blood. It would be years before the world would come to see just how wretched the Wales' union was.
When 30 years later, Kate Middleton made her own four-minute walk up the aisle of Westminster Abbey to trade haunting Chelsea's frock shops to be a working HRH, the numbers were stacked against her.
The house of Windsor might be splendid at many things – breeding horses, christening boats and keeping their Teutonic tidily hidden away – but on the marriage front, they have a truly appalling track record.
Prince Edward is the only one of the Queen's four children who has not been divorced and Princess Anne's son Peter Phillips became the first of Her Majesty's grandchildren to dissolve his union earlier this year.
So how in the name of Mischon de Raya, Diana's famous divorce firm, has Kate managed to pull off the royal coup of the century and made their marriage work?
In April this year the couple marked 10 years of marriage, releasing a slick, professionally-produced 'home movie' featuring the Cambridge family gambolling over sand dunes, all rendered in muted, co-ordinating hues and projecting cozy domesticity.
The answer, according to insiders, is two-fold.
To start with, they work well together – and I mean, work.
While Charles watched, dismayed and perturbed, as his new wife's popularity eclipsed his own, setting off years of the duo intractably locked in a game of one-upmanship, William and Kate have escaped following in his parents' sour footsteps.
"They've got a solid relationship and she gives him confidence," one friend who attended the couple's 2011 wedding revealed to The Times. "There is no jealousy, no friction, they are happy for each other's successes."
According to The Times, "In private William talks as passionately about Kate's work as his own campaigns, and takes pride in her growing confidence on the public stage."
Look at any photos of the couple out and about during an official engagement and it is clear that they are better together, a smiling, warm double act – the sum is greater than the aristocratic parts, if you will.
"Ultimately they are very much on the same side, on the same team. There is quite a lot of affectionate joshing between them but they have always had each other's backs," a source close to the couple told The Telegraph earlier this year.
"They are both very similar in the respect that they are intrinsically quite shy people who have sometimes struggled with life in the limelight," one royal insider has said. "When he is having a difficult time, she is the one who helps him through it but it works both ways. He is there for her and she is there for him."
Perhaps more interesting is how their partnership has affected William and given him the critical stability and groundedness that was lacking in his life for so long.
"Marriage maketh the man," a friend has told The Times. "Catherine's groundedness has been the critical anchor."
"Watching them over the past decade, they are the couple who finish each other's sentences," royal biographer Katie Nicholl has said. "As with any marriage, there have been ups and downs, but they have got through them. This is a marriage based on friendship."
That equality extends their home life where they reportedly balance their ever-growing royal workloads with raising their three children, with them taking it in turns and juggling diaries to ensure one of them always does the school drop offs and is there when they come home in the afternoon.
There is also something fascinating in considering the one thing that Kate gives William that no one else in his world ever has – a taste of normality. From their early years as a couple, he spent time with the Middleton family, reportedly even calling Michael Middleton, on occasion, 'Dad'.
There were Sunday lunch roasts (with William's favourite red wine on hand) and the duo even spent Christmas there on two occasions, skipping the elaborate, deeply formal royal celebration at Sandringham.
(Let's never forget the ruckus William set off in 2008 when, during his RAF training, he landed a military helicopter on the Middletons' lawn as part of a training flight.)
"[William] absolutely adores them. Michael is charming. Really kind, soft and gentle. William loves going to the country to stay with them. Their family life is so soothing for him as it's so different from his own family," a friend of the Middleton family said last year.
The centrality of his wife's family was only affirmed when two days after the birth of their first child George, they relocated to Michael and Carol's $9.4 million home Bucklebury Manor to spend their first few weeks acclimatising to parenthood.
Interestingly, one of the most significant ways his wife has proven to be a steadying influence on the future King William V is when it comes to dealing with the baying media.
Despite having spent years being chased, literally, by photographers around London, it was Kate who is reported to have been the one to push for a more strategic and sanguine approach.
"Where his relationship with the media was once all fury and frustration, he now understands using the power of modern media, so the public feel they're getting enough access," the same friend has said.
When the Cambridges became parents in 2013 welcoming son Prince George, it was Kate who reportedly decided to take a leaf out of Crown Princess Victoria of Sweden's book and to establish a compact with the press and the public. The royal house would doll out regular photos of the baby and in return would be able to enjoy a blessed peace that William was denied as a child.
A close aide told The Times, "For years, the battles around privacy and paparazzi intrusion were all consuming. He wanted to know, could we build them a credible plan allowing them a family life while slowly increasing the profile of official life? It took years to get there, but the success of that plan allowed him to be confident and content in his role. He's not worried about his kids' privacy any more and he has been able to be the kind of dad he wants to be."
The rare success that is William and Kate's partnership also lies in the fact that their priorities align perfectly.
"Kate understands that the only credo of the Royal Family is duty, duty, duty," one royal courtier told Tatler last year.
Which might sound simple on paper but the reality is far more demanding. Consider that less than 24-hours after giving birth for the first time she appeared in front of cheering, clapping crowds and a veritable wall of cameras that towered over the new family. Still, time and again she has approached daunting moments such as this with grace and poise.
Likewise in 2012. She and William were in Malaysia in the midst of a tour of southeast Asia to mark the Queen's Diamond Jubilee when topless photos of Kate, taken during the couple's recent holiday in France, were published.
Both the duke and duchess were "furious", according to biographer Nicholl, after being briefed about the situation by their private secretary, Jamie Lowther-Pinkerton, but she still put on an exemplary performance shaking hands and accepting flowers as they ploughed through the day's itinerary.
Thursday this week marked 40-years since Charles and Diana's wedding and it is impossible to not compare the two marriages, one defined by hurt and rancour and the other by their success as a consummate partnerships, both in public and at home.
Diana might have been a lamb to the slaughter on her wedding day but when Kate made that daunting, nerve-jangling four-minute walk down the aisle, looking back, she was actually a wolf in an Alexander McQueen gown. Thank god for that. I'm sure the Queen does.
- Daniela Elser is a royal expert and a writer with more than 15 years experience working with a number of Australia's leading media titles