King Charles emphasized the crucial UK-US partnership in a historic address to Congress, warning of global uncertainties. He received multiple standing ovations, highlighting the significance of his message.
Mentioned in this story
King Charles has stressed the value and importance of the "indispensable" UK and US partnership in an historic address to Congress in Washington DC.
In the historic setting of the Capitol building, the King warned that the two nations had to stand together in this "more volatile, more dangerous" era.
"We meet in times of great uncertainty, in times of conflict from Europe to the Middle East which pose immense challenges," he told the chamber, filled with US lawmakers.
It was the biggest diplomatic moment of his reign amid a backdrop of deepening political tensions between the US and the UK - and in the end, he got a standing ovation before he'd even spoken.
There were about 12 standing ovations in total, as the audience repeatedly interrupted the King's address with loud applause.
It might once have been taken for granted that the US and UK would be partners in defending democratic values.
But after recent tensions there seemed to be no such guarantees - and the King was here to rekindle that alliance, to an audience including US Vice-President JD Vance and political powerbrokers from both Republican and Democrat parties.
The King spelt out the cornerstones: there had to be support for Nato, "keeping North Americans and Europeans safe from our common adversaries". There needed to be backing for the "defence of Ukraine and her most courageous people".
Such speeches are written with the Foreign Office, and there was a clear message sent to US President Donald Trump, who has called for more military spending from US allies.
"Our country, in order to be fit for the future, has committed to the biggest sustained increase in defence spending since the Cold War," said the King.
The domed Capitol building looks part-temple and part-courthouse, appropriate for a speech that was strong on moral messages.
The monarch spoke of his own Christian belief, to loud applause, and his "faith in the triumph of light over darkness" and how that meant understanding other people's religions and beliefs.
"I am inspired by the profound respect that develops as people of different faiths grow in their understanding of each other," said the King, calling for peace, at a time of an unpredictable conflict in Iran and the Middle East.
The observation that "words carry weight and meaning" drew warm applause, as a message against the politics of wild rhetoric.
There have also been personal pressures on the King and Queen in this visit, in the toxic fall-out from the Andrew Mountbatten-Windsor scandal.
There have been calls for the King and Queen to meet survivors of the sex offender Epstein. That hasn't happened because of concerns about jeopardising the legal process.
The speech made a coded reference to such abuse, calling for support for "victims of some of the ills that so tragically exist in our societies today".
King Charles described the UK and US partnership as 'indispensable' and stressed the need for both nations to stand together in a volatile era.
King Charles delivered his speech at the Capitol building in Washington DC.
The audience interrupted the King's address with loud applause, resulting in about 12 standing ovations throughout the speech.
King Charles highlighted immense challenges posed by conflicts in Europe and the Middle East during his address.
At 93, Moira Brown will attend her fourth World Cup, celebrating Scotland's qualification for the tournament after nearly 30 years. She'll cheer for her team during their group stage matches in the U.S.
One in 17 children globally is involved in child labour, with many in hazardous conditions.
How Trump's immigration crackdown affected small-business loans for entrepreneurs.
Belfast residents voice disgust at riots following stabbing incident
One year on from the Air India crash, families like Sagar Patel's seek justice and closure.
Want a better skin care routine? Sign up for our one-week guide!
See every story in News — including breaking news and analysis.
There was also a reference to the gun attack in Washington DC at the weekend, which has seen a man charged with attempting to assassinate Trump and has raised security in the US capital to an even more intense level.
"Let me say with unshakeable resolve: such acts of violence will never succeed," said the King.
It's 35 years since the last time a monarch delivered such a speech to both houses of Congress, when the King's mother Queen Elizabeth II visited.
That had been in 1991, with the Berlin Wall knocked down, victory declared in the Cold War and liberal democracy in its most self-confident ascendancy.
Now the King had to be the cheerleader for such threatened values, talking of the need for an international rule of law and the importance of a shared belief in "democratic, legal and social traditions".
It was like a civics revision lesson in one of the great cradles of democracy.
With such shared historical and philosophical roots, "our two countries have always found ways to come together", said the King, as he warned against isolationism.
There was even room for a gag about the US being a young country, as it marks its 250th anniversary. "That's 250 years, or as we say in the United Kingdom, just the other day," the King said, getting a big laugh in response.
The chamber itself is a reminder of that younger heritage. With its brass rails and swing doors it has the feel of an old-fashioned department store.
After the rocky UK and US relationship of recent months, the King's challenging mission has been to repair some of the damage. He has used his own prestige - and Trump's fascination with monarchy - to try to rebuild a sense of transatlantic trust.
The UK visitors, including Foreign Secretary Yvette Cooper, will have been heartened by Trump's speech at the White House earlier in the day, with its celebration of a shared history between the US and UK and his recognition of the value of the military alliance.
That more positive mood music, and the thunderous applause in this chamber, will have encouraged the UK delegation that a corner could be turned. And so far, the trip has been projecting an optimism that's in contrast to awkward political moments with an unpredictable president.
In the King's words, it's been a "story of reconciliation, renewal and remarkable partnership". And he left the chamber to loud cheers, shaking hands on all sides.
Sign up here to get the latest royal stories and analysis every week with our Royal Watch newsletter. Those outside the UK can sign up here.