Where were you on May 19, 2018?
Like the JFK assassination or the moon landing or even Diana and Charles' wedding more than three decades earlier, an entire generation (at least) will be able to tell you exactly what they were doing on this particular a day – a day when a British Prince chose as his wife not some horsey blonde with a family tiara but electrifyingly a bi-racial, American divorcee.
Watching Harry and Meghan exchange vows felt like a watershed cultural and social moment that augured a new age for the royal family, chock full of diversity and inclusion.
This was not just a nation being totally seduced by this vast, wonderful spectacle of love and towering floral arrangements, this was a moment resonant with meaning.
And then slowly, gradually, everything fell apart. That 2018 bonhomie and joy has long since evaporated. Now, 22 months after that glittering moment, the Sussexes have departed royal life to set up shop in North America, leaving a nation with both a lingering sense of loss and a whiff of bitterness.
However, despite Meghan's tenure as a working HRH being one of the shortest in the last century or so, there is no question that the royal family has been indelibly changed by her presence.
Way back in 2018, nearly every story about her arrival on the scene trotted out obvious tropes about her being a "breath of fresh air" and a "modernising force". Her otherness as opposed to the standard Windsor bride template was held up as a thrilling landmark occurrence.
Essentially, Meghan's arrival on the Kensington Palace doorstep was heralded as exactly what the monarchy needed to blow away all the cobwebs and revamp its image for the Instagram age. Here was a woman who would embrace and fully use her platform in a modern, feminist way!
Looking back, I keep thinking there was just so much goddamn promise.
The biggest and most obvious Meghan effect was she generated the sort of global interest in the royal family the likes of which had not been seen for decades. The comparisons with Diana flew thick and fast and for good reason – she electrified crowds and made the royal family seem relevant and interesting.
Single-handedly (well, Harry did help too) she reshaped the perception of the Windsors from fusty Brits with balding pates and too many hats to being a nearly glamorous, alluring institution worth paying attention to.
And that is perhaps the greatest gift she ever gave the Queen and co – she made hundreds of millions of people interested in what is, if you think about it logically, a bizarre holdover from medieval Europe. That currency, of vast global public interest, is the life blood of royalty. Nothing sees a crowned head of state being forced to pack up their crowns and move to a middling rural four-bedder than public indifference and apathy.
More broadly, Meghan's tenure tested so many long held assumptions about the royal family, the primary one being that marrying into the institution was something to be universally desired.
In not even two years, the now 38-year-old shattered what lingering attachment women might have had towards the Cinderella fantasy.
Getting a Prince (or Princess) down the aisle was no longer about acquiring some wonderful gilt trappings, rather it was reframed as a terrible sacrifice of freedom and voice.
Likewise, Meghan flipped the narrative of the Prince saving the damsel.
If there is one thing I think the world can agree on when it comes to the Sussexes is that Meghan, with her unwavering love and support, was the one who swooped in to give Harry (who will always be the boy following his mother's coffin for so many) the security and succour he has long craved.
Like some sort of chemical experiment, what was so fascinating to watch was not so much how Meghan approached Windsor life but how the wider institution and Britain reacted to her presence in the royal midst.
She unwittingly forced the royal family and an entire nation to confront and debate racism in contemporary Britain, prompting a deeply uncomfortable national conversation about race.
Perhaps the most significant lasting impact of HRH Meghan, Duchess of Sussex, is that a truly modern woman, for the very first time, unintentionally tested the modern-day viability of the institution of the monarchy. The question of their very purpose and value was suddenly being debated – and in some instances affirmed.
When Harry and Meghan first announced in January they were planning on "transitioning" to a new model of royal life of their own conjuring, which would have seen them both still represent the Queen while also earning money from the corporate world, looking back, that was never going to fly.
However, that desire to find a way to reshape royal life into a more palatable, reasonable model is entirely fair.
For William and George (and George's firstborn) their lives are a fait accompli – investitures, pomp and having to spend an hour a week listening to the current PM blathering on.
But for Charlotte and Louis (and George's other children) the current model which they are meant to follow, the model that Harry and Meghan were meant to quietly accede to, seems more and more ridiculous and outmoded.
Prior to the advent of the Sussexes, the prevailing expectation was that Harry should be happy to accept a life of Duty and Responsibility, tempered with the benefits of a million-dollar lifestyle.
For every Spare down, the presumption was that they would cheerfully cede their personal agency and control over their lives in service of an institution whose social and political relevance is increasingly hazy.
To my mind, what Harry and Meghan initially suggested seemed like a hastily cobbled together ill-conceived wish list but they were right in wanting to find another way to be as HRHs.
When Charles ascends to the throne and his slimmed down vision of the monarchy comes into effect and William after him, they are going to have to find an answer to the lingering question of what to do with those not in the direct line of succession.
They can't expect the siblings of the King to be opening Midlands leisure centres and Liverpudlian recycling centres, and be jolly grateful about it all, for decades to come.
Ultimately, what the arrival of Meghan and the advent of the Sussexes did was to expose the fault lines in the modern monarchy and the fact that the expectations and privileges associated with membership are out of step with modern standards.
For example, the expectation that lower ranking members of the royal family should be happy with their B-grade lot of hand shaking and plaque-unveiling ad nauseam.
Ditto, it seems equally questionable whether it is fair that lesser ranking Windsors get the Sovereign Grant to pick up the cheque for part of their quite cushy existences.
These are all questions and issues that are not going to be addressed for years, if not generations.
When Meghan stepped through the Palace gates for the first time she set off a chain reaction, forcing the Windsors, and Brits wholesale, to start to confront questions about race, power, and the very structure of their society.
As of the time of writing, Meghan is back in Canada and the couple's new life, unleashed from any royal bonds, beckons. There is no question that her royal term will be the stuff of books, documentaries and PhDs for decades to come.
One concrete thing we can say about her royal legacy – she kicked off a reckoning that has been a long time coming, however how this will end remains a vast unknown.