As the Duchess of Sussex celebrates her birthday, Matthew Bell explains why the coming year could be her most pivotal yet.
Among rock stars, there is something called the "27 club". Its members are the poor souls who, for various reasons, never made it to 28.
They include Jim Morrison, Jimi Hendrix, Janis Joplin, Kurt Cobain and Amy Winehouse. Within the Royal family, there is something of a 37 club - though for very different reasons.
As the Duchess of Sussex, who turns 37 today (Saturday), will be glad to learn, it's the age at which female members of the Royal family are finally able to relax.
The path of a royal woman is not easy. Your late teens, twenties and even early thirties will be a maelstrom of insecurities and anxieties, made worse by unflattering pap shots and intrusions into your love life. But by the time you hit 37, you generally have your ducks in order and life is about to get a lot easier.
Take Zara Tindall, who, aged 37, has just given birth to her second daughter, Lena. She recently told a newspaper she had two miscarriages between the births of Lena and her first child, Mia, in 2014. Heartbreaking, and enough to make her beat a retreat from public life. Now she is back in the riding saddle, with a husband, two children and a home on the Gatcombe Estate. Sorted, as those maddening train station announcements like to say.
The Duchess of Sussex has spoken of her keenness to start a family, and 37 is an age at which royal women often give birth. Queen Victoria was a month shy of 38 when she had Princess Beatrice, her ninth and final child, in 1857. As was our own Queen when she gave birth to her fourth and final child, Prince Edward, in 1964.
It's hard to deny that there would be a neat symmetry for the Duchess of Cambridge - who was 36 when she gave birth to Prince Louis in April - if, like the Queen, she were to have a fourth aged 37.
There's also something symbolic about the number 37 for royal women. Victoria became Queen in 1837, only a month after turning 18, and went on to reign for 64 years. Another long-timer, Queen Elizabeth the Queen Mother, was crowned in 1937 - also becoming the last Empress of India - and turned 37 a few months later. Incidentally, she shares a birthday with Meghan, and would have been 118 today.
Princess Anne, the most senior female royal by blood after the Queen, was only awarded the substantive title of Princess Royal the year she turned 37. Why did the Queen wait so long to grant it? After all, it had been available since the death of the previous Princess Royal, Mary, Countess of Harewood, in 1965 (she was the eldest daughter of George V, younger sister of both Edward VIII and George VI, who married Henry Lascelles, Earl of Harewood).
It is possible that the title didn't pass to Anne sooner as Princess Margaret was, in theory, also entitled to it. But Anne has certainly earned it in the years since, becoming the hardest-working royal: last year, she clocked up more days' service than anyone, and she is on course to do the same again this year.
So what is 37 likely to look like for Meghan? For most royal women, it is a period of domesticity. Princess Anne was not doing nearly as much work when she was 37. She was still married to Captain Mark Phillips and had two small children, though she did join the International Olympic Committee.
Princess Margaret was also in a period of relative calm at that age. It was 1967, she had two young children and her marriage to Lord Snowdon was going well - so well that she allowed him to take a notorious portrait of her, in which she appears to be naked.
The Queen was pregnant with Prince Edward for most of her 38th year though, as fans of The Crown will recall, she wasn't exactly able to enjoy her maternity leave: Harold Macmillan was gravely ill for much of 1963, which required her to appoint a new prime minister, Alec Douglas?
Home, in October. She was also 37 during the turbulent events of the Profumo affair and the JFK assassination.Indeed, 37 hasn't always been a good year historically for royal women. Queen Elizabeth I was 37 when she learned of the plot to kill her by a Florentine banker, Roberto Ridolfi, and replace her with the Catholic Mary, Queen of Scots. This led to the execution of Mary's suitor, the Duke of Norfolk, and, years later, that of Mary herself.
In more recent times, though no less sensationally, Sarah, Duchess of York, was stripped of her HRH title in 1996, shortly before her 37th birthday. This was easily the most hurtful part of her divorce from Prince Andrew that year. Alone among royal women today, she probably doesn't look back at 37 with much love.
Which leads us to the most significant royal we have yet to consider. For Diana, Princess of Wales, 37 was an age she would never know. It was two months after her 36th birthday that she died in that Paris car crash, nearly 21 years ago. Looking back, it's almost incredible to consider how much she packed in to so short a life, and what a lasting effect she had - and yet, in many ways, she remains the benchmark for royal brides, up to whom we hold Meghan and Kate as comparisons.
Prince Harry has said he thinks of his mother every day. "Depending on what I'm doing, I wonder what it would be like if she was here, and what she would say, and how she would be making everybody else laugh. Who knows what the situation would be, what the world would be like, if she were still around?"
Today, as he and his wife celebrate Meghan turning 37, Diana will doubtless be more present than ever. The good news is that Harry is finally sorted, and that for Meghan, 37 could be a year of peace and joy that Diana never had.