US President Joe Biden appeared to break royal etiquette rules during a visit to Windsor Castle on Monday when he met with King Charles.
The President of the United States was snapped touching Charles' arm and putting his hand on his back, which should not be done unless the royal initiates the contact first.
However, a Buckingham Palace source has revealed to People magazine that Prince Charles was “entirely comfortable” with the greeting.
“What a wonderful symbol of warmth and affection it was between both the individuals and their nations,” the source said.
Former royal butler Grant Harrold previously told Insider that members of the public must always wait for a royal to initiate a handshake.
"A royal handshake should consist of two-to-three pumps, with your palms open and thumbs down," Mr Harrold said. "If you are a member of the public meeting a member of the royal family, you should never offer your hand to shake — wait for them to initiate the handshake."
According to Mr Harrold, this is due to security reasons, "As well as an etiquette rule, it poses a major security risk if someone is able to get so close that they are able to touch members of the Royal Family."
Former First Lady Michelle Obama famously made the mistake of touching the late Queen on the back after being briefed on correct royal protocol. However, she later revealed Her Majesty herself told her the protocol was 'rubbish'.
Former President, Donald Trump, was also ridiculed online when he walked in front of the Queen during his meeting with her, with royal watchers gasping at the faux pas.
It would seem as though these rules have been broken more and more in recent times, as royals' interactions with the public become less traditional.
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