Diana was the embodiment of a Disney princess, just as Kate Middleton and Meghan Markle were after her. Anyone can be President but you can't be a King or Queen without being born to royalty, or marrying in. It's the unattainability of that status that draws such fascination. They're almost mystical figures.
Wherever I am in the world and I speak to a member of the public after they have met a royal, their most common response is: "They're so normal!" As if they aren't real until you actually come face-to-face with one.
That's why Markle is such a star. She was normal and now she isn't. She's part of the fantasy. If you look into her trolls online many just come across as jealous. Many others appear to be supportive of her and what she represents. On the day her engagement to Harry was announced, an African American colleague told me she couldn't believe someone like Markle had "penetrated" the royal family.
The same excitement came through on the Facebook feed of an edition of my show "CNN Talk" that I anchored from Buckingham Palace. One of the panelists, Ayesha Hazarika, an equal rights campaigner, told me, "The royal family are the absolute top of the British class system; it is the most elitist system on the planet. A lot of people of color will think "good: it's high time that this system was opened up a bit more."
The institution has modernised, though you'd be forgiven for not noticing. The Queen went with tradition to marry a fellow blue-blood in Philip (a Greek and Danish prince) but Prince Charles married outside royalty to aristocrats. William cast his net further with Kate Middleton who was from a middle-class, rural family.
went further afield to marry an American divorcee
. The last time that happened was in 1936 when Edward VIII had to abdicate his royal title in order to marry his American divorcee, Wallis Simpson. Meghan Markle though has been embraced by both the royal and political establishment which shows how things have moved on, if glacially.
Prince Harry is unlikely ever to be king so he is under less pressure to conform than his elder brother, though he did still require permission from The Queen to marry Markle. He is particularly close to William and Kate so he will have significant influence on the way the monarchy develops, as will his wife.
The "Fab Four" as they have been dubbed by the UK tabloids, co-ordinate their work through their court at Kensington Palace. When Harry moved in years ago, a royal source told me the office had been set up with a corporate structure. The "principals," as they are known, are treated as joint CEOs. Courtiers are there merely to advise.
William, Kate, Harry and Meghan call the shots, which was perhaps a reaction to the system the boys were brought up in when aides exercised more control, to the frustration of their mother Diana. The four are also equal partners in The Royal Foundation which brings together their charitable and campaign work.
"Working as a family does have its challenges," conceded Harry at a Foundation forum in February 2018. He and William have had a lifetime to get used to that of course but not so for Middleton and Markle.
The world's media turned out in force for the forum because it was our first opportunity to hear how Markle might take her public role forward. She had only been engaged to Harry for a few months and all we knew was that she had given up her acting career and cut all ties with the campaigns and organizations she had been associated with such as UN Women and World Vision.
Royal sources assured me she had every intention of continuing her work on those issues but wanted to do so with a clean slate from her new, more high-profile position.
Markle was asked on stage about women finding their voice and she responded, "You'll often hear people say, 'Well you're helping women find their voices,' and I fundamentally disagree with that because women don't need to find their voice. They have a voice. They need to feel empowered to use it and people need to be encouraged to listen."
It was a clear statement of intent from Markle that she wasn't going to stop having opinions just because she was joining the most famous family in the world.
People would probably have questioned her strength of character if she had done anything else but she did raise a few eyebrows when she added, "and I think right now in the climate that we're seeing, with so many campaigns, with 'Me Too,' 'Time's Up,' there's no better time than now to continue to shine a light on women feeling empowered, and people really helping to support them, men included."
#MeToo and #TimesUp are regarded by some as political movements which is territory royals are expected to avoid and this speaks to the challenge Markle now faces.
She's eloquent, passionate and charismatic and that's endeared her to many but could create jealousy within the ranks, as Diana learned. If she then crosses the line into what could be construed as political interference then republicans will use it against her, increasing pressure on the family.
How would it go down if Markle repeated her views on Donald Trump, for example? During the 2016 US election campaign, she told The Nightly Show with Larry Wilmore, "Yes of course Trump is divisive," and then went on to call him "misogynistic." She said she "might just stay in Canada" if Trump won the presidential election, which of course he did.
As a senior member of the royal family, Markle is expected to represent the monarch, potentially even hosting President Trump. That role is only tenable if she avoids party politics. Who knows who she will be asked to meet by government in future?
Prince William: "I blubbed when George was born"
... A motto often attributed to Elizabeth is, "I have to be seen to be believed," and that explains why she wears those bright colors that mark her out in the crowd. When she meets a member of the public, she typically asks if they have come far and by the time they have answered an aide has ushered her on.
She's created a memory for life for that person but, crucially, hasn't given away anything of herself. She's also created a powerful image for the media to use showing her amongst the people. This was the monarch who popularized the royal walkabout and it wasn't by accident.
The Queen created more opportunities to get out there and meet people when she formalized the support of voluntary service in to her job description. It allowed her and her family to link up with charities and causes they care about and show some character.
Without that, The Cambridges and Prince Harry wouldn't have been able to start the "Heads Together" campaign to reduce the stigma of mental illness which has had a palpable effect on attitudes in the UK.
The brothers used it as an opportunity to open-up about the trauma of losing their mother. "Our grandparents, The Queen and The Duke of Edinburgh, had made support for charity central to their decades of service to the nation and the Commonwealth," The Duke of Cambridge told the Royal Foundation forum.
"The task for us would not be to reinvent the wheel. Instead, our job was to follow the example of those who had come before us, to hold on to the values that have always guided our family, but also to seek to engage in public life in a way that was updated and relevant for our generation." In other words, to continue the conversation his grandmother picked up on.
William gave a demonstration of that "updated" monarchy when he left hospital with his wife and newborn son and heir, Prince George, in July 2013. He had his sleeves rolled up and carried the car seat himself, clicking it in to position before driving off with his new family.
That doesn't sound extraordinary but just a generation ago, when Prince Charles did the same thing with William as a baby he wore a suit and tie and took the back seat of the car as a chauffeur drove them all off.
I interviewed William a couple of weeks after George's birth at Kensington Palace. He was still in that exhausted yet elated stage of early fatherhood. "I blubbed for about half an hour when George was born," he told one of the producers. "It was ridiculous."
I then asked him about his approach:
William: Where I can be, I am as independent as I want to be, same as Catherine and Harry. We've all grown up differently to other generations and I very much feel if I can do it myself, I want to do it myself. And there are times when you can't do it yourself and the system takes over or it's appropriate to do things differently. But, I think driving your son and your wife away from hospital was really important to me. And I don't like fuss, so it's much easier to just do it yourself.
Prince Charles: Pushing the envelope
... In ordinary life, Charles would have retired years ago. His challenge has been to find his own purpose and he's managed that by professionalizing his own role, embracing the "public service monarchy" with thousands of engagements and fundraising efforts.
He's pushed the envelope, literally, on the family's political neutrality too by writing a series of so called "black spider" memos to government ministers with his thoughts on policy, so-called because of The Prince's unique scrawl. He's expressed views on everything from climate change to urban planning ...
A royal source assures me he has every intention of following her (the Queen's) example and steering clear of expressing opinion in public when he does accede to the throne. He's aware that, as Head of State, he will be expected to act on the advice of his ministers, not on his conscience.
Until then though, he has some room for manoeuvre perhaps and he's arguably been proven right on some of the issues he pioneered as a young man such as environmentalism and inter-faith dialogue that have since gone mainstream.
Charles' character famously came into question when his affair with Camilla Parker-Bowles came to light, followed by an acrimonious divorce from Diana. He paid tribute to the "brilliant" way his second wife took on the "real, real challenge" of defining her public role in an interview I did with him in Scotland, 2015. It's still not clear if the public is ready to have Camilla as Queen, though she will automatically receive the title on his accession.
Clarence House issued a statement in 2005 saying she would use the title of "Princess Consort" instead but my understanding is nothing will be confirmed until the day Charles becomes king.
When I hear talk of the crown passing straight to The Duke of Cambridge, I don't detect any appetite from either of them for that to happen. The Prince of Wales has spent a lifetime preparing to rule and The Duke is busy coming to terms with his own clout and juggling a young family.
Neither of them speaks publicly on the matter of succession for obvious reasons but both will be aware of the towering example they are expected to live up to in Elizabeth II. She kept herself at the heart of the national conversation and that's the cachet that underscores her clout.