For centuries, it has just been the done thing: the royals call their father’s ‘Papa’.

The 11-year-old Princess Elizabeth did it in adorable fashion when she wrote for her mother and father an account of their 1937 Coronation.

King Charles referred to his father Prince Philip as ‘my dearest Papa’ after his death in 2021 – and King Edward VIII used the term to refer to George V.

Now, Prince William‘s three children – Prince George, Princess Charlotte and Prince Louis – have called their father ‘Papa’ as they celebrate his 42nd birthday.

The Princess of Wales released a sweet new portrait of her husband and their children leaping in the air, with a caption that reads: ‘Happy birthday Papa, we all love you so much!’

Etiquette expert William Hanson told MailOnline that the use of ‘Papa’ is a ‘class thing’ that is echoed by members of the aristocracy and upper classes – but added that there may also be an element of tradition that has maintained it within the Royal Family.

For centuries, it has just been the done thing: the royals call their father’s ‘Papa’. The 11-year-old Princess Elizabeth did it in adorable fashion when she wrote to her mother and father after their 1937 Coronation

King Edward VIII always referred to his father George V as ‘papa’ in his correspondence. In a letter he wrote to his mother Queen Mary on the day of his scandalous abdication in 1936, Edward mentioned his late ‘papa’. Above: The pair in 1904, when Edward was a young naval cadet

In 1937, Princess Elizabeth referred to her parents – King George VI and Queen Elizabeth – as ‘mummy and papa’ when she wrote them a six-page account of their Coronation.

The 11-year-old future Queen wrote in red crayon on the first page, ‘To Mummy and Papa’, and then said on the line below: ‘In Memory of Their Coronation’.

She added: ‘From Lilibet, By Herself’.

The loving term was also used in the other direction.

When Princess Elizabeth and her new husband Prince Philip were on their honeymoon in 1947, King George VI referred to himself as her ‘devoted Papa’.

He wrote in a letter: ‘I have watched you grow up all these years with pride under the direction of Mummy, who as you know is the most marvellous person in the world in my eyes, & I can, I know, always count on you, & now Philip, to help us in our work… I can see that you are sublimely happy with Philip, which is right, but ‘don’t forget us’ is the wish of your ever loving and devoted Papa.’

Similarly, King Charles often referred to both his parents as ‘mama’ and ‘papa’.

After Prince Philip’s death in April 2021, he told the nation: ‘My dear Papa was a very special person who I think above all else would have been amazed by the reaction and the touching things that have been said about him and from that point of view we are, my family, deeply grateful for all that.’

Now, Prince William’s three children – Prince George, Princess Charlotte and Prince Louis – have called their father ‘Papa’ as they celebrate his 42nd birthday. The Princess of Wales released a sweet new portrait of her husband and their children leaping in the air

The caption read: ‘Happy birthday Papa, we all love you so much!’

And after the Queen’s death in September 2022, he used the nicknames for both his parents.

In a video broadcast, he was close to tears as he finished his message by saying: ‘And to my darling Mama, as you begin your last great journey to join my dear late Papa, I want simply to say this: thank you.

‘Thank you for your love and devotion to our family and to the family of nations you have served so diligently all these years. May “flights of Angels sing thee to thy rest”.

Last year, Princess Charlotte showed how she too has taken on the royal tradition when she spotted her father appearing on stage at the Coronation concert in Windsor.

The then eight-year-old shouted to her brother Prince George: ‘Look! There’s Papa!’

Mr Hanson said: ‘It is a class thing. But it is probably also just one of those royal eccentricities that has evolved over time,’ he said.

‘Dad and Mum are a bit clunky. We know that the English aristocracy like names that end in an A sound. Sarah, Camilla, Papa. Dad and Mum is a bit common basically.’

Prince Charles pays tribute to ‘dear Papa’ hours after father’s death

Prince Philip seen with his son Prince Charles in 1956 as he prepared to depart for his Commonwealth tour

For Father’s Day earlier this month, Prince William referred to Charles as ‘Pa’. Sharing a throwback photo of him playing football with his father in 1984, he wrote: ‘Happy Father’s Day, Pa’

He added: ‘They will have all grown up hearing it as perfectly normal. They probably haven’t stopped to give it any thought to be honest.

‘The Royal family, and the English in general are not necessarily ones to advocate change.’

For Father’s Day earlier this month, Prince William referred to Charles as ‘Pa’.

Sharing a throwback photo of him playing football with his father in 1984, he wrote: ‘Happy Father’s Day, Pa’.

King Edward VIII always referred to his father George V as ‘papa’ in his correspondence.

In a letter he wrote to his mother Queen Mary on the day of his scandalous abdication in 1936, Edward mentioned his late ‘papa’.

The document was quoted from by historian Alexander Larman in his 2021 book The Crown in Crisis: Countdown to the Abdication.

Edward said: ‘I loved our last few minutes together and at last being able to bring dear Papa into our talk.

‘We were different in many ways and yet you know how devoted I was to him and I cried when you said he was human.’

Attempting to defend the constitutional upheaval he had caused by choosing to give up the crown so he could marry divorcee Wallis Simpson, Edward again referred to his father.

He told his mother in the same letter: ‘It was a big thing to do but I know it will be best for all in the end and Bertie will make a find king and will be able to carry on without any upset and will find that I have left the Crown and the Throne as Papa left it on the same high level it has maintained for so many centuries.’

Nearly three decades earlier, in November 1910, when Edward had only months previously become the heir to the throne following the death of his grandfather, he opened a letter to his father with the words ‘Dear Papa’.

In 1728, the seven-year-old Bonnie Prince Charlie – who famously tried and failed to seize the throne as an adult – referred to his father as ‘Papa’ when he wrote to him after being told off for upsetting his mother

After telling him what newspapers he was reading, he added: ‘It is ever so much more interesting for me to follow the political proceedings now, that I have been taught something of the country’s constitution…’

But the use of ‘Papa’ stretches much further back than the 20th century.

In 1728, the seven-year-old Bonnie Prince Charlie – who famously tried and failed to seize the throne as an adult – referred to his father as ‘Papa’ when he wrote to him after being told off for upsetting his mother.

The future royal rebel – grandson of King James II – said: ‘Dear Papa, I thank you mightily for your kind letter. I shall strive to obey you in all things. I will be very dutifull to Mamma and not jump too near her…’