Melania Trump dresses
US President Donald Trump and US First Lady Melania Trump walk with US Ambassador to the United Kingdom Woody Johnson (L) as they arrive at the US ambassador's residence Winfield House in London on July 12, 2018.BRENDAN SMIALOWSKI/AFP/Getty Images

US President Donald Trump has finally arrived in the United Kingdom for the highly publicised 4-day visit. Apart from meeting British Prime Minister Theresa May, the controversial protest-laden trip also includes a meeting with Queen Elizabeth and a private weekend in Scotland.

The official visit comes days after Trump said the UK economy is in turmoil because of the trade policies.

Trump himself is facing the backlash from global leaders for his inhumane immigration policies. Anti-Trump protesters are expected to campaign in many parts of the country including Bristol, Newcastle, Leeds, Cambridge and Cardiff.

Permissions have already been granted to fly a 19-foot-tall 'baby Trump' orange balloon in Central London.

U.K. Activists Inflate Giant Baby Donald Trump Balloon In Preparation For U.S. Presidential Visit
UK activists inflate giant 'baby Trump' balloon in preparation for US presidential visit.

Amidst all these hiccups, it looks like nothing can stop the American President from meeting Queen Elizabeth. However, royal watchers wouldn't be surprised if Trump breaks some of the royal etiquettes while meeting the monarch.

So what can possibly go wrong? If you're not familiar with the royal protocol, many things, actually. Here we pick out five key royal protocols that Donald Trump might default on.

The Trump handshake: Remember the Trump handshake? Well, that would be the last thing anyone would expect from the President when meeting Her Highness. According to the royal protocol, the visitor should wait until the Queen offers her hand for the handshake and then they should shake it politely. So it's a big 'NO' to Trump's over-the-top handshake. And of course, hugs and kisses are strictly prohibited.

The Queen should lead the way: The President should always allow the Queen to lead. For example, if they are walking around, the Queen should lead and the rest should follow. Well, we seriously wonder if the ever-active President can follow someone patiently.

How to address the Queen: Though it is not necessary for the President and the First Lady to bow before the Queen (as they are non-British citizens), there are certain protocols to be followed while addressing the Queen. When beginning a conversation, the visitor should address her as 'Your Majesty' and then use the term 'Ma'am.'

It can be noted that Trump broke the diplomatic protocol by calling German Chancellor Angela Merkel by her first name. South African President Nelson Mandela once called the Queen by her first name but that was on friendly ties with the British monarch, which Trump is yet to earn.

It's a strict no-phone zone: The Queen strictly operates on a no-phone zone. Neither the President nor the First Lady can operate their mobiles while meeting the Majesty.

Trump's controversial Brexit statement: Just days before his UK visit, the US president made a controversial statement warning the British prime minister that a soft Brexit exit will put the trade relationship with the US in turmoil. Trump also added that May is letting down voters with her "business-friendly" Brexit plan.

The statement has truly kickstarted a new row of controversies and it is said that the Queen has passed a strict order not to mention Brexit during the President's visit.

Well, with many royal protocols and etiquettes, and a giant 'baby Trump' orange balloon flying over London, it would be interesting to see how the US president will handle the situation.