Donald Trump is famed for saying and acting exactly how he likes and while the US President has already met the Queen, there is specific Royal protocol he must follow.
ITV News spoke to former Royal butler Grant Harrold to get a few hints and tips for Mr Trump.
The US president will visit the UK for three days before an overnight stay in Ireland, and here are some things he really mustn't do.
Don't take charge
The most important rule that Mr Trump can stick to, is to let the Queen lead - this applies to everything, from the topic of a conversation to where they're walking, to when a meal has ended.
The Queen is always in charge.
Donald Trump might have been elected President of the US, but the Queen is the Queen and should be treated with deference.
Don't bow from the waist
Since neither the US President or his wife Melania are British citizens, they do not have to bow or curtsey to the Queen, but it's still a nice thing to do.
Should Mr Trump feel like giving a little bow though, this is all it should be: little.
The bow should be a neck bow, not a waist bow - which is what you do when you've finished a theatrical performance.
If the First Lady does give a curtsy, this is simply the right foot behind the left with a slight bob.
Don't offer a handshake
After (perhaps) giving a little bow on meeting the Queen, the President should not, under any circumstances, offer his hand for a handshake.
The Queen doesn't always shake hands with people, but if she wants to, she will offer her hand (that point about letting the Queen lead again), at which point the President (who has in the past seemed to need some guidance on handshake etiquette) should accept and pump up and down two or three times.
Mr Trump shouldn't grip the 92-year-old's hand too hard, nor should he clasp it with the other hand as well, or shake too vigorously.
After the handshake, the President's hands should return to his sides.
Don't call the Queen Liz
This would probably be the ultimate mistake.
When you first meet the Queen, the correct way to address her is "Your Majesty", and then after that it's "Ma'am" (pronounced like ham).
When ending a conversation or leaving, you can revert back to "Your Majesty" for the final time.
Don't touch the Queen
Other than shaking the Queen's hand, there should be no other physical contact between Mr Trump and the Queen.
This includes touching someone on the arm when talking to them, or guiding them when walking.
There should definitely be no hand-holding à la Theresa May.
Don't lead the conversation
When talking to the Queen, Mr Trump should let her begin the conversation and also lead it.
This will ensure the exchange does not go off track, into personal matters, or things the may not wish to discuss.
Don't talk about politics
One of the topics the Queen will not wish to discuss is politics, so Mr Trump must not talk about this with the Queen.
All members of the Royal Family are politically neutral, so engaging them in a conversation about politics would be a very big blunder.
Safer topics of conversation the 72-year-old could involve the monarch in are things such as the weather (as a Brit the Queen will probably enjoy this) or the Royal corgis.
Don't sit down before the Queen does
The 45th US President should not sit down before the Queen does, and he should not remain sitting if the Queen stands.
Mr Trump should only take a seat if the Queen offers one, and as she stands again, he should too.
Don't turn your back on the Queen
When walking with the Queen, she should always be slightly ahead, solving the problem of showing the Queen your back.
However, once Mr Trump has had an audience with the Queen and is leaving a room, he should not turn immediately turn his back on the monarch and leave, instead, he should take a few steps backwards, and then it is acceptable to turn around and walk forwards to exit the room.
At one point in history it was unacceptable to show a Royal your back and people would would backwards when in the presence of one.
This rule has been relaxed in recent years, but it would still be possible for Mr Trump to walk in a sort-of-sideways manner so as not to show the Queen his back, but also see where he's going.
Don't eat before the Queen does and don't finish after her
During the visit to Buckingham Palace, Mr Trump will enjoy a state banquet with her Majesty.
However, the one major he should follow (other than not sitting down before the Queen does) is to not start eating before the Queen does.
Similarly, once the Queen has finished eating, he should finish eating too.
It doesn't matter if they've only had one bite out of a dainty cucumber sandwich, once the Queen is done, you are too, and the course will be cleared.
Moreover, as Mr Harrold explains, the correct pronunciation of the controversial cake rhymes with "gone".
Yet so long as he doesn't tuck in before the Queen, the other rules probably aren't too hard and fast.
Don't worry about being sent to the Tower of London
The Queen is known to be a lot more relaxed regarding Royal protocol than many of her successors, so any rule breaking will not see Mr Trump immediately carted off to the Tower Of London as they might have done in years gone by.
Besides, it's a visitor attraction these days anyway.