The Royal Family is a global institution and everyone from the King to The Princess of Wales is expected to follow protocol - but exceptions can and have been made.
Prince Philip, Duke of Edinburgh was renowned for his no nonsense approach to royal duties. While there are countless examples to choose from, one story from 2016 highlights this attitude.
The Queen was greeted by President Barack Obama and First Lady Michelle Obama in 2016 when they travelled to Windsor Castle for lunch in celebration of her 90th birthday.
Royal author Robert Hardman subsequently revealed how the Queen and Prince Philip took on the US Secret Service and won.
The late Duke of Edinburgh was determined that he wanted to drive the Obamas personally despite the President's security team refusing.
Speaking to BBC News, Mr Hardman said: "The Obamas wanted to come and be the first non-family people to say Happy 90th birthday to the Queen when she turned 90 in 2016.
"They flew in by helicopter to Windsor Great Park and the royals wanted to pick them up in the park where they landed. But the Secret Service said, 'no, we're the only people who drive the president' and it went right to the top.
"It's the only time in the entire Obama presidency when the couple were driven by someone other than a White House agent, they were driven by Prince Philip with the Queen in the back with Michelle."
It was later revealed that the First Couple's security detail were "terrified".
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Another special moment between the Royal Family and the Obamas was seen during their first state visit to Buckingham Palace in 2009.
While standing next to each other at a small reception, Michelle opted to put her arm around the monarch.
To everyone's astonishment, the Queen reciprocated the gesture and placed her gloved hand on the former First Lady's back. Protocol dictates that you should refrain from touching the royals, unless they initiate the contact.
In 2018, Michelle spoke about why she put her arm around the Queen and what happened afterwards in her best-selling memoir, Becoming.
She said: "The Queen glanced down at the pair of black Jimmy Choos I was wearing. She shook her head. 'These shoes are unpleasant, are they not?'
"She gestured with some frustration at her own black pumps. I confessed then to the Queen that my feet were hurting. She confessed that hers hurt, too.
"We looked at each other then with identical expressions, like, when is all this standing around with world leaders going to finally wrap up? And with this, she busted out with a fully charming laugh."
