The King is to tell Congress today that while the UK and US have not always agreed on everything, the nations’ shared traditions mean that “time and again, our two countries have always found ways to come together”.
The monarch’s remarks in a speech to both houses on Tuesday will be seen as a tacit acknowledgement of recent transatlantic strains over the Iran war, which have put Donald Trump and Prime Minister Sir Keir Starmer at loggerheads.
Charles is also expected to make brief reference to the shooting at a Washington dinner attended by the US president on Saturday night and in a show of solidarity and support offer “the highest regard and friendship of the British people to the people of the United States” on the 250th anniversary of American independence.
A man has been charged with the attempted assassination of the President and security around the King and Queen’s visit is extremely high.
The speech by the King will be only the second time a British monarch has addressed a joint meeting of Congress, the first being the late Queen Elizabeth in 1991.
It will be a key moment in the schedule on the second day of Charles and Camilla’s four-day state visit to the US. They will also be guests of honour at a White House banquet.
In a nod to recent tensions, which have seen Trump lambast Britain, Charles will reflect that while the UK and US have not always agreed on all matters over the past 250 years, the foundations of their “democratic, legal and social traditions” – stretching all the way back to the Magna Carta – are such that “time and again, our two countries have always found ways to come together”.
He is also set to point out how the US and UK have stood together through moments that have defined their shared history and that “our defence, intelligence and security ties are measured not in years but in decades”.
Against the backdrop of global uncertainty and the challenge it poses, the King is also expected to say that by defending and reaffirming these common values and ideals, both nations can promote security and prosperity both now and in the future for the benefit of the world.
And talking about his own faith, he will express his belief that in the hearts of the two countries lies “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”.
Charles is also set to reference the importance of the trade and technology deals that will play a vital part in the countries’ continued economic partnership, while also hailing America’s many natural wonders, and stressing how important it is to defend and protect “nature’s own economy”.
He is expected to conclude by noting that the story of both nations over the last 250 years is one of “reconciliation and renewal”, giving rise to “one of the greatest alliances in human history”, which he hoped would continue to safeguard their shared values long into the future.
The speech, which is written on advice of the Government, is expected to last 20 minutes.

The King and Queen arrived in the US mid-afternoon local time on Monday, landing at Joint Base Andrews in Maryland.
They then met President Trump and First Lady Melania at the White House, followed by a garden party.
The two couples greeted each other outside by the historic building’s south portico overlooking the lawns where past presidents have hosted Queen Elizabeth II.
Camilla wore a brooch pinned to her chest featuring the American stars and stripes crossed with the Union flag.
The trip is a significant diplomatic visit for the King which the UK government hopes will ease tensions with the president.
It also marks the first time a reigning monarch has visited the US in almost 20 years, with the last occasion a trip by Queen Elizabeth II in 2007.

Waiting at the bottom of the steps of the plane was a line of dignitaries prominent among the was the UK’s ambassador to America Sir Christian Turner, who replaced Lord Peter Mandelson when he was sacked over new revelations about his relationship with sex offender Jeffrey Epstein.
The state visit has “all appropriate security measures” in place following a suspected assassination attempt on Trump, the ambassador said earlier.
Charles and Camilla received posies from children of British military families based in the US, before being greeted by the diplomatic, federal and state representatives and walking through an honour cordon formed by US military personnel.
Before they left Joint Base Andrews, a military facility on the outskirts of Washington, a military band played the national anthems of the UK and US.
At the garden party with around 650 guests at the British Embassy the King chatting to former Olympic diving champion Tom Daley about their shared love of knitting.

Camilla spoke to leading figures from domestic abuse charities and in a lighter moment confessed to feeling “jet lagged”.
Charles and Camilla are not able to meet victims and survivors of paedophile Jeffrey Epstein during their four-day visit due to ongoing legal cases, including the arrest of the King’s brother Andrew Mountbatten-Windsor.
Michelle DeLaune, chief executive of the National Centre for Missing and Exploited Children, praised the Queen as “wonderful” for “raising awareness” and getting “dialogue going”.
She added: “There are many people suffering in silence and having people, someone like her, to look up to gives a sense it’s not so isolating.”

Asked about whether the King and Queen should have met victims and survivors of Epstein, she said: “I think it has to be a choice of individuals, for King and Queen.
“I think the voices of victims and survivors are not only heard but progress made, we will continue working to ensure we are bringing voices loud and clear.”
Minor adjustments have been made to some royal engagements following the shooting at the White House Correspondents’ Association dinner.

Security teams in Britain and the US worked through the night assessing the state visit after the president was endangered when shots were fired outside the dinner.
Britain’s ambassador in Washington, Sir Christopher Turner said UK and US security teams had been planning the trip for weeks before the incident at the media dinner, with changes possible “as we go”.
While minor adjustments will be made to one or two royal engagements, the overall plan is understood to remain unchanged.
Buckingham Palace confirmed the visit would “proceed as planned” after discussions were held on both sides of the Atlantic and advice taken from the Government.