Prince Harry reportedly calls his sister-in-law 'Cath' - a nickname derived from her full name Catherine Middleton, OK! magazine has claimed.
Harry and Kate are known to be particularly close, with Harry asking his sister-in-law for her approval before asking Meghan t marry him.
And now the Duchess of Cambridge is reportedly getting much closer to Meghan in an effort to take the American-born Duchess under her wing.
Those who are regular watchers of The Crown, you'd know that Prince Philip likes to refer to his wife as 'Lilibet.' It's also been said that he calls her 'sausage' when they are alone.
Her Majesty's great-grandchildren Prince George and Princess Charlotte like to refer to the Queen as 'Gan-Gan,' while William jokingly called her 'Gary' when he was young after struggling with the pronunciation with 'Granny.'
High society gossip columnist Richard Kay in the Daily Mail, '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'.’
Prince George and Princess Charlotte also apparently have a sweet nickname for Camilla.
The Duchess of Cornwall told Lady Gaga at the 2016 Royal Variety Performance that her grandkids call her 'Gaga'.
Prince Harry sweetly calls his father 'pa' and is often called 'darling boy' in return. This was demonstrated at the prince's wedding, when Prince Charles walked Meghan Markle down the aisle, Harry could be heard thanking his 'pa' and Charles sweetly replying.
Meghan Markle has also been given her own inner circle moniker.
It's been reported that Prince Charles is said to call his daughter-in-law Tungsten, inspired by the tough metal known for its robustness.
According to the Mail, the nickname came from Meghan’s strength and determination, which impressed her new father-in-law.