From His Royal Highness to the Duke of Cambridge, there are many ways to address Prince William.
But of course, to his children, he is just their dad and they don't need to bother with the formalities.
In fact, Prince George even has a sweet nickname for him - and it was once let slip by the Duchess of Cambridge.
It came to light when Kate was chatting to well-wishers on a visit to Leicester City Football Club in 2018.
Kate and William were at the club to pay their respects to the club's chairman Vichai Srivaddhanaprabha, who died in a tragic helicopter crash.
According to PEOPLE, one football fan, Fiona Sturgess, asked Kate how her three children Prince George, Princess Charlotte and Prince Louis were doing.
And Fiona later told reporters: "Kate said that William was playing football with the children last night and one of them said, I think it was George, ‘Are you playing football tomorrow, Pops?’ ”
But Pops isn't the only nickname that appears to be used in the Cambridge household.
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Shortly after he was born it was revealed Kate and William started calling Prince George PG - his initials.
Eventually, they added the word Tips - after the famous teabag brand - but then tweaked the name again to just Tips.
And in 2019, Prince William appeared to call Princess Charlotte by a most adorable name.
In a rare family video clip, William and Kate were joined by their children at the Royal Chelsea Flower Show.
Kate had helped to design a garden for the show and George, Charlotte and Louis came along to have a look.
While playing on a swing in the garden, William called out to his daughter, asking her to come and give him a push.
But instead of saying 'Charlotte', he called for 'Mignonette'. The French word is said to mean "small, sweet, and delicate" or "cute".
Meanwhile, it seems Kate has gone by a series of cute yet funny nicknames over the years.
According to OK! Magazine, Prince Harry doesn't call her 'Kate', but instead refers to his sister-in-law as Cath.
As well as Catherine, Kate and Cath, the duchess is also frequently called 'babe' and 'darling' by her husband, 'mummy' by her children and while at school she was known as 'Squeak'. The latter was derived from the name of her guinea pig.
