Following the pomp and pageantry outside the White House, the King and Mr Trump had a private meeting in the Oval Office. In pictures taken ahead of the meeting, the US President could be seen placing his hand on the monarch’s knee as they both appeared to be laughing.
Mr Trump raised eyebrows on Monday again after he appeared to pat the King’s back after their initial meeting in Washington.
While not an official royal rule, it is generally thought that it should be avoided initiating physical contact with a member of the Royal Family unless they offer it first.
However, in recent years, the royals have been more keen to breach the code and have been seen physically interacting with members of the public on many occasions.
According to the Royal Family’s official website, there are no obligatory codes of behaviour when meeting the King and Queen or a member of the Royal Family, but many people wish to observe the traditional forms.
For men, this is a neck bow (from the head only) whilst women do a small curtsy. Other people prefer simply to shake hands in the usual way.
On presentation to the King, the correct formal address is ‘Your Majesty’ and, thereafter, ‘Sir’.
On presentation to The Queen, the correct formal address is ‘Your Majesty’ and subsequently ‘Ma’am,’ pronounced with a short ‘a,’ as in ‘jam’.
For male members of the Royal Family, the same rules apply, with the title used in the first instance being ‘Your Royal Highness’ and subsequently ‘Sir’.
For other female members of the Royal Family, the first address is conventionally ‘Your Royal Highness’ and subsequently ‘Ma’am’.