With Prince Harry and Meghan Markle's romance heating up, speculation is rife that a royal engagement could be on the cards.
But if the Prince did go down on one knee, what would that involve? Suffice to say, it would go a fair way beyond a quick "we're getting married!" text.
Keep reading below to see the seven rules of etiquette bound up in a proposal by the fifth in line to the British throne.
Harry and Meghan's first hurdle lies in a law that dates back to the 18th Century. The Royal Marriages Act 1772 requires members of the Royal Family to obtain permission from the sovereign to marry.
This rule stipulates that all descendants of George II must obtain the sovereign's agreement before they wed, otherwise the marriage is invalid.
If issued, the permission of Queen Elizabeth II will announced by means of an ornate notice of approval - an "Instrument of Consent" - featuring elaborate calligraphy, gold braiding and the Queen's majestic red wax Great Seal of the Realm.
Pomp and circumstance
The formal consent notice will be hand-decorated with motifs that are seen in some way to reflect the happy couple.
Kate Middleton was represented by a white lily in the permission issued for her and Prince William's engagement in 2011, while her husband-to-be was symbolised via a Welsh leek.
The language will vary depending on its subjects, but we can expect it to be suitably flowery and reverential.
The Queen's notice in 2011 gave permission to "Our Most Dearly Beloved Grandson Prince William Arthur Philip Louis of Wales K.G. and Our Trusty and Well-beloved Catherine Elizabeth Middleton".
The question of divorce
Some commentators have pondered how the fact that Meghan is a divorcee will affect the Queen's consent. The royal family has had a chequered history on the issue of divorce, with Edward VIII famously abdicated the throne in 1936 in order to marry divorcee and love of his life, Wallis Simpson.
But the Queen did grant permission for son Prince Charles to re-marry the Duchess of Cornwall in 2005 (both were divorced at the time), even going so far as to provide him with a ring that had belonged to his fervently anti-separation grandmother.
The move was seen as a softening in attitude from the Queen, who was involved in the decision of her own sister, Margaret, not to marry an officer she fell passionately in love with in the Fifties - because he was divorced.
All in a phone call
While the Queen's written permission of a royal engagement is a formal affair, the asking of it may be slightly less so.
Prince William did so in a phone call, after he had asked Kate (on safari in Kenya), and just a day before their engagement was publicly announced.
In practice, it's very unlikely that the Queen would refuse her permission for an engagement - the only exception may be if she were advised to do so by a sitting prime minister.
Many couples now dismiss the tradition of asking for permission for the bride's hand in marriage from her father as outdated and sexist.
But it's unlikely, given the formality of a royal engagement, that Harry would eschew this step.
However, he may follow in brother William's footsteps and ask for permission from Tom Markle after proposing to Meghan.
Meghan's nearest and dearest and Prince Harry's close family - including his father Prince Charles, his mother-in-law the Duchess of Cornwall and his brother and sister-in-law, Prince William and the Duchess of Cambridge - are also likely to be informed of the engagement prior to a public announcement.
The odds are on that Prince Harry will pop the question using a family heirloom ring, in keeping with royal tradition.
Prince William famously popped the question to Kate with a striking oval blue 18-carat sapphire and diamond ring that belonged to his mother, Princess Diana.
The Queen herself received a ring from Prince Phillip that was fashioned from diamonds taken from his mother's tiara.
Or Harry may follow his father Prince Charles' example and encourage Meghan to pick out her own ring. The royal family's favoured firm, Garrard Jewelers, provided rings for Princess Diana and Princess Anne.
Alternatively, he may take the lead from his cousin Zara Phillip's husband Mike Tindall, who romantically designed his own ring for his betrothed, which featuring a single solitaire diamond.
The royals have form when it comes to popping the question - but with beautiful homes and a large holiday budget, they also have the armoury.
Prince William proposed to Kate on holiday, in a "rustic and ultra-private" log cabin nestled amid the foothills of Mount Kenya.
According to Kate, it was a "very romantic" moment. And in the grand tradition of nervous grooms-to-be everywhere, William said he felt relieved after carrying his mother's ring around in his rucksack with him for three weeks prior to the event, as he decided on the best moment.
The Queen herself is also thought to have given the green light to marriage with Prince Philip on holiday - albeit one rather closer to home.
It's understood he popped the question during a three-week grouse and stalking holiday at the royal estate of Balmoral in 1946 (a trip he undertook upon invitation from the Queen Mother).
Prince Charles popped the question to Diana during a private dinner at Buckingham Palace, while another of the Queen's grandchildren, Zara, was proposed to at the home she shares with rugby partner Mike in Gloucestershire.
As Meghan has declared her love of globe-trotting - "I love to travel, and I travel so often," she said in an interview with Good Housekeeping - we think Harry could do worse than a foreign holiday proposal.
And don't forget the hand-written love note, Harry; "the idea of someone taking the time to put pen to paper, I think, is what really matters," Meghan says.
It's customary for royal brides and grooms-to-be to inform the sitting prime minister of their decision before it is announced to the public.
This isn't compulsory but it's seen as a nice touch.
Then PM David Cameron was informed of Kate and William's engagement in 2010, just moments before it hit headlines around the world.
Cameron recalled how he was told the happy news via note passed to him during a Cabinet meeting. "There was a great cheer that went up and a banging on the table," he says.
He then called William to personally pass on his congratulations and spoke to reporters from the steps of no. 10, declaring, "It's great to have a piece of unadulterated good news that everyone can celebrate and be happy for them."
As Harry is fifth, rather than second, in line to the British throne, the protocol surrounding this may be slightly relaxed. On the other hand, the fact that it will be global news will give an incentive to inform the Prime Minister ahead of time.
If Harry and Meghan get engaged, a formal announcement will be issued from either Kensington Palace (the official communications base for him, Prince William and the Duchess of Cambridge), Clarence House (Prince Charles' spokespeople) - or Buckingham Palace.
Given the royals are now fully represented on social media platforms, the statement will probably be released simultaneously across Twitter, Facebook and Instagram.
This will be followed by official reaction from all parties close to the couple - including Meghan's family, Prince William, Prince Charles and the Queen.
Politicians and other public figures will be quick to share their congratulations on social media channels.
A TV interview could be in the works and if so, it'll be set up fairly quickly, in order to manage global media interest over the announcement.
Harry and Meghan may choose someone they're familiar with to conduct this; as Prince William and Kate did in 2010 with ITV's Tom Bradby, whom they regarded as "a friendly face".
The last thing on Meghan and Harry's immediate to-do list after getting engaged will be to choose a date and a venue for the occasion.
While many other logistics caught up in arranging a wedding - the dress, the guest list, the honeymoon - can wait, courtiers will be keen to get this detail nailed down quickly.
Not only will it allow royal aides to plan ahead more effectively, it will again help in handling the glare of the media spotlight. The date will be set within a year of the engagement announcement (a longer arrangement would be too loose for the stringent protocol of royal engagements).
As for venues, the happy couple will have their pick of prestigious British buildings steeped in history.
The glorious, 700-year-old Westminster Abbey is the obvious choice, with the Queen, the Queen Mother and most recently Prince William all having tied the knot there.
The iconic dome of St. Paul's, where Charles and Diana wed in 1981, is another option.
Windsor Castle could also be a venue for Harry and Meghan to mull over, although the fact that it is based outside of London - thereby not allowing for a ceremonial procession - makes it less likely.
This article first appeared on Grazia Daily
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