Donald Trump gave King Charles a pleasant three-word instruction after the monarch reportedly asked him: "What do I do next?"

The exchange was captured by a lip reader during this afternoon's White House arrival ceremony, where Charles and Queen Camilla were welcomed with a 21-gun salute before the national anthems were performed.

According to expert Jeremy Freeman, Charles asked the US President: "What do I do next?"

Standing alongside their wives on the South Lawn stage, Trump is said to have responded: "Enjoy the scene. It's very nice here. You can sit down now. I'm gonna make a speech."

The lip reader also revealed that Charles then enquired: "Shall I sit down for this."

Trump replied "yes" before delivering a speech in which he paid tribute to Queen Elizabeth, describing her as a "very special woman".

Addressing the bond between the UK and the US, he declared: "We see today a living symbol of this centuries' old bond. Just a few dozen feet to the left where I stand – there her late Majesty Queen Elizabeth, an incredible woman who I had the privilege of getting to know.

"Queen Elizabeth, the second, very, very special woman, who is very greatly missed on both sides of that mighty Atlantic, long ago planted a young tree. It was a very young and beautiful tree and look at it now." Charles and Camilla are on day two of their state visit to the United States, in what has been described as a hugely important diplomatic mission which will try to repair a "special relationship".

The visit is unfolding against a backdrop of strained ties between Britain and America over conflicts in the Middle East.

This marks the first British state visit to America since 2007, when Queen Elizabeth II was welcomed by President George W. Bush.

The royal visit also coincides with the approaching 250th anniversary of American independence from Britain.

Charles and Camilla touched down yesterday for the four-day trip, which kicked off with a private tea at the White House with Trump and First Lady Melania.

Trump will be expected to adhere to two strict protocols while hosting the royals, according to historian Geraldine Roberts, who told us: "Strict protocols also apply at state functions where guests wear formal attire and the heads of state are seated together at the top table."

Regarding the second protocol, she added: "Gifts are another important ceremonial feature and should carry a message of goodwill. It will be interesting to see what the King and the president give to each other.

"During Queen Elizabeth's state visit in July 1976, she presented President Ford with a soup tureen featuring a painted image of the White House, and in return she received a bronze statue by Harry Jackson of cowboy Calyton Danks astride his horse Steamboat."

However, Trump has already faced accusations of breaching protocol after placing a hand on the King's arm as they made their way towards the White House yesterday. Some maintain that nobody should initiate physical contact with the monarch.

Nevertheless, The Royal Family's website clarifies that no such obligatory code exists in relation to meeting the King.

It says: "The King and Queen meet thousands of people each year in the UK and overseas. Before meeting Their Majesties, many people ask how they should behave. The simple answer is that there are no obligatory codes of behaviour - just courtesy."

Charles is also scheduled to deliver a speech to Congress to reaffirm the Anglo-American alliance.

In his 20-minute address, he is anticipated to emphasise that "time and again" the UK and the US have discovered ways to come "together".

He will also articulate that the hearts of the two nations share "a generosity of spirit and a duty to foster compassion, to promote peace, to deepen mutual understanding and to value people of all faiths and none".

Geraldine, who has authored two historical biographies, outlined why the state visit holds such significance.

She said: "Many British people believe that the monarchy is outdated and of no value. But the monarchy are our most important assets when it comes to diplomatic missions.

"While our politicians are feuding, the King and Queen are looking beyond the current turmoil and trying to preserve friendly Anglo-American relations.

"They are conveying friendly sentiments to the people of America at an important milestone in their history, as they celebrate 250 years of independence."

Prior to Charles's arrival in the US, Trump lavished praise upon the man who had hosted him the previous year, describing him as a "great gentleman" and a "wonderful wonderful person".

There had been speculation that the royal visit might not proceed as scheduled following an attempted incident at a White House Correspondent's Dinner.

Nevertheless, before touching down on American soil, Charles and Camilla reached out to Trump to express their sympathies.

A palace spokesman also confirmed the couple were "greatly relieved" Trump and Melania were unharmed.