US President Donald Trump is to finally meet the Queen.

The monarch – an expert in diplomacy – has met all manner of controversial world leaders during her 66-year reign.

Donald Trump Donald Trump during a signing ceremony with North Korea in Singapore (Kevin Lim/The Straits Times/PA)

But how will the American leader fare when he encounters Britain’s head of state?

  • The handshake

Mr Trump has form for grabbing hands and holding on to them for an extraordinarily long time.

He has been described as approaching a handshake like an arm wrestle, in which he clasps the hand and pulls sharply, leaving the recipient off-balance.

Taoiseach visits United States of America Irish Taoiseach Leo Varadkar shakes hands with US President Donald Trump (Niall Carson/PA)

He yanked French President Emmanuel Macron’s hand at the Bastille Day celebration in July 2017, holding on to it for nearly 30 seconds.

At the White House in April 2018, he also led the French leader away from reporters after shaking his hand and keeping hold of it.

Prime Minister Theresa May also encountered Mr Trump’s unusual mode of dealing with foreign leaders.

They held hands as they walked along at the White House during their first meeting in January 2017.

Mrs May later said the US president was “actually being a gentleman”.

“We were about to walk down a ramp, and he said it might be a bit awkward,” she said.

The Queen is, however unlikely to accept any extended hand-holding.

  • No Touching

Although Buckingham Palace insists there are no obligatory codes of behaviour when meeting the Queen, it is a generally accepted custom that you do not touch the monarch other than shaking hands if she puts out her hand to greet you in this way.

That means no hugs, air kisses – unless you are family – or arms around the back or shoulder.

The QueenFormer Canadian cyclist Louis Garneau puts his arm around the Queen as they pose for a photo (Kirsty Wigglesworth/PA)

The Queen is unlikely to take offence, although tactile behaviour is not encouraged.

In 1992, the then Australian premier Paul Keating was dubbed the “Lizard of Oz” after cameras caught him giving the Queen a helping hand at Canberra’s Parliament House by touching her back.

Former Canadian cyclist Louis Garneau also once put his arm round the Queen in 2002 as his wife took a picture of them together while the monarch was touring Canada.

But the Queen appeared not to mind and smiled broadly for the camera.

  • The Obamas

It will be difficult for Mr Trump to improve upon the rapport the Queen has with former US president Barack Obama.

The Queen and the ObamasBarack Obama and his wife, Michelle, talk with the Queen and the Duke of Edinburgh at Buckingham Palace in 2009 (John Stillwell/PA)

They developed such a friendly relationship that Mr Obama even dropped in to see the sovereign the day after her 90th birthday, describing her as “one of my favourite people”.

The Queen also showed her sense of humour when she and Prince Harry appeared in a video to promote the Invictus Games, responding to a mock challenge from the Obamas with a comical “Oh really”.

Ahead of the G20 summit in 2009, the Queen and First Lady Michelle Obama dispensed with protocol and acted like old friends when they put their arms around each other at Buckingham Palace.

The Queen and Michelle ObamaMichelle Obama and the Queen put their arms around each other at a reception at Buckingham Palace (Daniel Hambury/PA)

No other members of the royal family will meet Mr Trump at Windsor Castle, nor join him for tea, Buckingham Palace said.

But what do the royals think of the American billionaire-turned-politician?

  • The Duchess of Sussex

Meghan was, before marrying into the royal family, a vocal critic of former reality star Mr Trump, backing his rival, Hillary Clinton, and suggesting before the 2016 election that she would leave the US if he won.

Royal Ascot – Day One – Ascot RacecourseMeghan has previously been critical of Donald Trump (John Walton/PA)

She previously labelled the billionaire “divisive” and a “misogynist”.

On a leaked tape from 2005 which surfaced during Mr Trump’s presidential campaign he was heard making lewd remarks about women.

“When you’re a star they let you do it. You can do anything,” Mr Trump said, adding later: “Grab them by the pussy. You can do anything.”

  • The Duke of Sussex

According to Meghan’s father, Thomas Markle, Harry urged Mr Markle to give Mr Trump a chance.

INVICTUS GAMES 2017First Lady Melania Trump and Prince Harry at a bilateral meeting ahead of the 2017 Invictus Games in Toronto (Danny Lawson/PA)

The duke’s father-in-law shared details of their private conversation in an interview with ITV’s Good Morning Britain.

He said: “Our conversation was I was complaining about not liking Donald Trump, he said ‘Give Donald Trump a chance’.

“I sort of disagreed with that.”

Harry has already met the First Lady, Melania Trump, while in Canada for the Invictus Games in 2017.

  • The Duke of Edinburgh

Philip is known for his plentiful gaffes.

But the 97-year-old duke has retired from public duties, meaning Mr Trump and the First Lady will not be treated to any of his famous quips.

  • The Duke and Duchess of Cambridge

William is unlikely to be impressed with Mr Trump’s previous comments about his mother.

Mr Trump once said he would have slept with Diana, Princess of Wales, without hesitation.

William, Diana and HarryThe Princess of Wales and her two sons, Prince William (left) and Prince Harry (Martin Keene/PA)

In a Howard Stern radio interview recorded just months after the princess died, he also branded her “beautiful” but “crazy”.

Mr Trump used to bombard Diana at Kensington Palace with massive bouquets, according to broadcaster Selina Scott, who said he saw the princess as “the ultimate trophy wife”.

She added that Mr Trump gave Diana the creeps: “It had begun to feel as if Trump was stalking her.”

Mr Trump also made remarks about Kate after she was photographed sunbathing topless by the paparazzi in France.

“Kate Middleton is great – but she shouldn’t be sunbathing in the nude – only herself to blame,” he wrote on Twitter.

  • The Prince of Wales 

Heir to the throne Charles is a passionate advocate of multi-faith tolerance and an environmental campaigner on climate change.

The Prince of WalesThe Prince of Wales has been an impassioned campaigner on the environment (Arthur Edwards/The Sun/PA)

While the prince has called climate change “the wolf at the door”, Mr Trump has called it a “Chinese hoax” and “bullshit”.

Mr Trump pulled the US out of the Paris climate agreement — the only country to do so – saying it disadvantaged America.

  • The  Duke of York

Andrew shares a love of golf with the American leader.

The Duke of YorkThe Duke of York during The Open Championship 2016 at Royal Troon Golf Club, South Ayrshire (Peter Byrne/PA)

Mr Trump is a huge fan of the sport and owns golf resorts in Scotland.

  • The Princess Royal

Anne – known for her no-fuss approach – would have been seen as taking no nonsense from Mr Trump if they were meeting.

Princess AnneThe Princess Royal at Minchinhampton Rugby Club in Gloucestershire (Steve Parsons/PA)

The hard-working princess, who has devoted herself to public duty, has been described as aiming to serve, but not to please.