Watch: Kate Middleton Addressed Prince Charles Using His Unofficial Title During the G7 Summit
They might officially start their titled names with His or Her Royal Highness.
But Royal Family members have surprisingly affectionate nicknames for one another behind closed doors.
At a reception at the Eden Project held for world leaders by the Queen, the Duchess of Cambridge greeted Prince Charles by saying "Hello Papa" showing she has picked up the name her husband William uses for his father.
Lilibet, the Queen's childhood nickname, is arguably the most famous royal pet name, as Harry and Meghan have chosen it for their daughter's name.
Here are some of the royal nicknames we know about.
As a child the Queen, then Princess Elizabeth, is said to have been unable to pronounce her own name well, instead saying 'Lilibet'.
The adorable mispronunciation became a nickname which was first used by her grandfather, King George V.
It stuck with the rest of her family too, and then became the name by which Prince Philip referred to her.
Harry and Meghan chose to name their daughter Lilibet Diana after she was born on 4 June, and said the decision was made with the Queen's support.
Gary, or Gan-Gan
The Queen has many an official royal title, but it's a different story at home.
According to royal correspondent Richard Kay, Prince William was encouraged to call her Granny as a child, but he couldn't quite get the hang of it.
What he could manage, was Gary.
Kay said: "On another occasion, the Queen was on hand after William fell over at Buckingham Palace, bawling: ‘Gary, Gary’. A guest who went to help asked who Gary was, assuming it must be a member of the royal household.
"‘I’m Gary,’ explained the Queen, as she scooped him up. ‘He hasn’t learned to say Granny yet.’"
He doesn't still call her Gary, but his children had similar problems with working out what to call her.
Kate revealed when Prince George was a toddler he called her Gan-Gan.
Another one for the Queen, used by her late husband Prince Philip.
It was reported in 2006 in The Sunday Times that Philip had referred to his wife as 'cabbage'.
The nickname was used in the Peter Morgan film The Queen, which was released the same year.
Morgan said: "I inquired in royal circles and was told on very good authority that that is what the duke sometimes calls the Queen."
Not quite a nickname but it seems Prince Charles is generally known as Papa to his children and in-laws.
Harry has referred to his father as Papa in speeches in the past, and on arrival at a join engagement in Cornwall in June 2021, it was easy to spot the moment Kate used the same name for him.
Usually in public the royals refer to one another by their titles or by their full names, but Kate looked to be overcome with excitement at seeing her father-in-law before the true formalities of the evening began.
The name has been passed down the generations too, as a Mother's Day card shared by Kensington Palace on Instagram in March 2021 showed that Charlotte calls Prince William 'Papa' too.
Haz and H
Meghan Markle appears to prefer not to address her husband by his usual name of Harry, which is already a nickname, as he was christened Henry.
In an interview in 2019, Meghan revealed to ITV's Tom Bradby that she called him 'H', and in 2021, as the prince toured LA with James Corden, she referred to him as 'Haz'.
Meghan is often referred to as Meg by friends, and Haz was spotted referring to her by this shortening back in April 2018.
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Fred and Gladys
These nicknames, used by Charles and Camilla for each other, were a big part of The Crown, season four, on Netflix.
The nicknames were apparently first used by them when they dated briefly in their twenties.
But when Charles was set to marry Diana, he is said to have given Camilla a bracelet with 'GF' engraved on it, meaning Gladys and Fred.
Princess sisters Eugenie and Beatrice are very close.
Eugenie often shares touching messages to her sister Beatrice on Instagram around birthdays or when the royal has big news.
Eugenie uses Bea or Beabea when referring to her big sister, and often accompanies it with an emoji, of a bee, of course.
Beatrice is less open on her social media, so we may never know how she refers to her little sister.
Lottie, or Mignonette
Princess Charlotte is already racking up royal nicknames from her parents.
Her mother was overheard referring to her daughter as 'Lottie' while on an engagement in Northern Ireland.
Kate's also been heard calling her daughter 'poppet'.
But the grandest nickname comes from her father who calls her 'Mignonette'.
In a video of the family of five playing in the Duchess of Cambridge's Chelsea Flower Show garden, he was heard calling "Mignonette", which Charlotte responded to with a "yeah?".
It might come from the French word Mignon which means small and delicate.
PG or Tips
According to Vanity Fair, Prince George is referred to by his initials, PG at school in Thomas's, Battersea.
It was then reported that his parents had decided to play with this and called him PG Tips, after the tea brand, or just Tips.
The Sun also reported that a dog walker who bumped into George when he was with his grandmother Carole Middleton in Berkshire, shared another nickname the young royal had.
According to the dog walker, George told her: "I'm called Archie."
While many people still call the Duchess of Cambridge Kate, apparently her brother-in-law Harry decided he wanted his own name for her.
He was reported to have started calling her Cath, an alternative shortening of Catherine.
She was quizzed about it in 2017 during an interview on BBC Radio 1.
Presenter Scott Mills put the nickname to her and while she did not confirm it - she also didn't deny it.
"I’m not sure, I’m not that familiar with it," Kate told Scott Mills. "I'll answer to most things though."
Prince Charles started calling the Duchess of Sussex 'Tungsten' in her early royal days, according to the Daily Mail.
A source said: "Prince Charles admires Meghan for her strength and the backbone she gives Harry, who needs a tungsten-type figure in his life as he can be a bit of a softy. It’s become a term of endearment."
The nickname came because he saw Meghan as strong and unbending, like the rare metal, apparently.
One of the most famous royal nicknames belongs to Sarah Ferguson, who has been known as Fergie for years.
Even as the Duchess of York, the title she was given when she married Prince Andrew, she has more commonly been known as Fergie.
It was revealed to also be a family nickname when Meghan used it during her interview with Oprah Winfrey in 2021.
Recalling learning how to curtsy before having a meal with the Yorks and the Queen, she said: "Right in front of the house we practiced and ran in. Fergie ran out and said, 'Do you know how to curtsy?'
"Apparently I did a very deep curtsy, I don’t remember it, and then we sat there and we chatted."
Princess Diana called her oldest son Wombat, according to Prince William himself.
He confessed to the nickname from his late mum in 2007 when he was interviewed by NBC.
He said: "It began when I was two. I've been rightfully told because I can't remember back that far.
"But when we went to Australia with our parents, and the wombat, you know, that's the local animal. So I just basically got called that. Not because I look like a wombat, or maybe I do."
Showing that sometimes a general term of affection is all that's needed, the Duchess of Cambridge reportedly once called her husband 'babe' in public.
While the couple were at the Chelsea Flower Show in 2016, William was asking about a Buxus plant, to which Kate is said to have told him: "Babe, we've got those. We've got loads of those."
Perhaps the duchess was exasperated by her husband's lack of green fingers.