"Whatever our differences, whatever disagreements we may have, we stand united in our commitment to uphold democracy, to protect all our people from harm, and to salute the courage of those who daily risk their lives in the service of our countries," Charles told US lawmakers during a rare speech to a joint meeting of the US Senate and US House of Representatives, and after a prolonged standing ovation at his entrance with Queen Camilla.
Charles' address came on the second day of a four-day state visit during a tense time in relations between the two countries, after US President Donald Trump has repeatedly criticised UK Prime Minister Sir Keir Starmer for what Trump says is his lack of help in prosecuting the Iran war.
"I come here today with the highest respect for the United States Congress - this citadel of democracy created to represent the voice of all American people to advance sacred rights and freedoms," Charles said.
"The alliance that our two nations have built over the centuries, and for which we are profoundly grateful to the American people, is truly unique," he said.
"And that alliance is part of what Henry Kissinger described as Kennedy's 'soaring vision' of an Atlantic partnership based on twin pillars: Europe and America."
Before his speech, Charles met with top Republican and Democratic lawmakers after a morning visit to the White House with Camilla that included a closed-door meeting between the King and Trump.
The events are part of a visit to the US designed to underscore ties forged between the UK and its former colony over the 250 years since American independence.
Earlier, during a ceremonial outdoor reception at the White House, Trump stressed the friendship that has evolved between the two peoples since their days as adversaries during the War of Independence and the "wounds of war" it caused.
"The soldiers who once called each other Redcoats and Yankees became the Tommies and the GIs who together saved the free world as brothers in arms and brothers in eternity," the president said in a reference to World War II.
"What a beautiful British day this is," Trump told the gathering under an overcast April sky to the amusement of the guests from the UK.
Trump and the King then huddled in the Oval Office for a meeting that was closed to the public, reducing the potential for the freewheeling and sometimes controversial meetings with foreign officials that have become routine during Trump's second term.
After escorting the King and Queen to their limousine for departure from the White House, Trump told reporters, "It was a really good meeting. He's a fantastic person. They're incredible people and it's a real honour."
Addresses to joint meetings of Congress are generally reserved for the closest US allies or major world figures.
The last was by Israeli Prime Minister Benjamin Netanyahu, in July 2024.
Trump's administration has repeatedly criticised many NATO members for not offering more assistance to US operations against Iran and pressed European countries into sharing more of the financial burden for supporting Ukraine against Russia's invasion.
While written on the advice of the UK government, much of the language and tone in the speech came from Charles himself, a Buckingham Palace source said.
with AP
