When was the last time you saw the Queen and Prince Philip kiss in public, or Prince William and Kate hold hands? Some royal watchers might assume that etiquette or royal protocol prevents couples from indulging in PDA. But that's not the case. Rather, the royals choose to remain professional when they are out and about because they are working representatives of the British monarchy.
In the case of Prince William and Kate, HELLO! magazine's royal correspondent Emily Nash explains: "The Duke and Duchess are almost always seen in photographs taken during official engagements so they are at 'work' and it would be unprofessional to hold hands. They also need to shake hands with a huge number of people as they meet then, so aside from being on duty, it wouldn't be very practical!
"We know they are very affectionate and that sometimes comes across during more light-hearted moments, at sporting events or similar, but you wouldn't expect them to put that on show while in more formal situations."
The most senior royals in the family need permission from the Queen to marry. As outlined in the Royal Marriages Act 1772, any potential bride or groom for senior royals require the official stamp of approval from the monarch. All eyes are currently on Prince Harry and Meghan Markle, with a big announcement expected any time soon.
"Prince Harry is one of the first six people in line to the throne, so he does need the Queen's permission to marry," says Carolyn Harris, a royal historian and author of Raising Royalty: 1,000 Years of Royal Parenting.
An announcement of the couple's happy news via Kensington Palace would soon follow, though Harry, who is fifth in line to the throne, may decide not to host a formal press briefing like the one held after the announcement of his brother Prince William's engagement to Kate in 2010.
Christmas at Sandringham
In the same vein, only couples who are engaged or married are invited to spend Christmas with the Queen at Sandringham. Her Majesty hosts a more intimate meal for the closest members of her family at her country home, but in the days leading up to Christmas, she will also throw a bigger Christmas lunch at Buckingham Palace where distant relatives make the guest list. And in keeping with tradition, you'll often see the Queen and her family attend church on Christmas Day.
While there is no official rule in place, heirs should technically not take the same flights to protect royal lineage. Of course, to be practical, you will have seen direct heirs travelling together in the past countless times before but they must seek permission from the Queen, who has the final say on the matter.
Prince William and Prince George have flown together on their royal tours to Canada, Australia, New Zealand and most recently Poland and Germany. Similarly, when William was a tot, he accompanied his father Prince Charles on worldwide tours.
You can probably count on one hand how many times a royal has willingly stopped to pose for a selfie with a fan. In the spirit of goodwill, Prince William once obliged a schoolgirl by taking a selfie with her on Christmas Day at Sandringham in 2014.
But generally speaking, royals politely decline photographs as they are often focused on an engagement when out in public, and in their working capacity. The times when you will see them in a selfie is when they've accidentally photobombed one.
Last year, Prince Harry admitted that he "hates selfies". During a visit to the Australian War Memorial in Canberra, he turned down the request of a young fan, explaining: "No, I hate selfies. Seriously, you need to get out of it (the habit), I know you're young, selfies are bad. Just take a normal photograph!"
The Queen has also previously revealed that she finds it "disconcerting" and "strange" when she is faced with a sea of people trying to take selfies with her. The implication was that Her Majesty considers it bad manners for wellwishers to be looking at a screen when she makes public appearances as a guest. She confided in US ambassador Matthew Barzun, who told Tatler: "She was essentially saying: 'I miss eye contact'."
On occasion, we'll see royals signing their names in a guest book or on special notes, such as messages attached to wreaths. But you will never see them sign autographs for fans during a walkabout. A long-standing rule remains in place for all royals, because of the risk of the signature being forged. Prince Charles has previously been heard turning down a fan, politely saying: "Sorry, they don't allow me to do that."
Pack an all-black outfit when going abroad
Royal protocol dictates that members of the royal family must pack an item of black clothing when going on royal tour, in the unfortunate event that someone passes away when they're abroad. As a rule, all members of the royal family must wear black when mourning as a mark of respect.
Throughout history, the rule has been honoured by various members of the royal family. Back in 1992 when Princess Diana's father, Lord Spencer, died, the Princess of Wales was away in the Alps skiing with Prince Charles. On their way back, the royal couple followed suit and dressed in all-black attire.
This hasn't always been the case, however. When the Queen's father, George VI, died in 1952, she was in Kenya on safari with Prince Philip, and didn't have a mourning outfit ready. As a result, she wasn't allowed to be photographed until a suitable outfit had been brought to her.
No political views
By law, the Queen is entitled and well within her rights to vote. There is nothing written in British law barring her from taking part in an election, but it just isn't the done thing. According to the UK parliament website: "Although not prohibited by law, it is considered unconstitutional for the monarch to vote in an election."
On the royal family's official site, Her Majesty's unbiased role in Parliament is explained further. As Head of State, the Queen is expected to "remain strictly neutral with respect to political matters, unable to vote or stand for election." This is why you'll never hear the Queen or members of the royal family airing their political views in public.
And it goes without saying, royals are not allowed to hold a political office, to safeguard against any monarch using their influence to sway political opinion or laws.
Bowing and curtseying
When greeting the monarch, men are required to bow to the Queen while women traditionally curtsy. The gestures don't need to be long or exaggerated – a subtle bow or curtsey will do.
How to sit like a royal
Although not technically a rule, it's generally frowned upon for female royals to sit with her legs crossed at the knee. Legs and knees must be kept together, which means crossing at the ankle is fine.
Kate's go-to position appears to be "the Duchess slant", where she keeps her knees and ankles tightly together and slants her legs to one side. They make the legs appear longer and are a more modest position. Princess Diana was known for sitting in the same exact way when out on engagements.
How to hold a teacup
Only on occasion will you see members of the royal family sipping on tea in public, even though they do love their tea time. The correct etiquette is to hold the top of your cup handle with your thumb and index finger and only sip from the same spot, to avoid multiple lipstick stains. And lastly, remember to keep your pinky in.