Britain's King Charles III has urged the United States to stand firm with its Western allies, as strains over Iran and Ukraine risk undermining transatlantic ties facing their most serious test in years.
"The challenges we face are too great for any one nation to bear alone," he said in a speech at the US Congress, calling for partners to defend shared values.
"Whatever our differences, whatever disagreements we may have, we stand united in our commitment to uphold democracy," the monarch told lawmakers.
Addressing Congress during celebrations marking 250 years since American independence from Britain, Charles stressed the historic ties between the two nations, saying their partnership was "born out of dispute, but no less strong for it."
"I pray with all my heart that our alliance will continue to defend our shared values ... and that we ignore the clarion calls to become ever more inward-looking," he added.
He said "unyielding resolve is needed for the defence of Ukraine and her most courageous people - in order to secure a truly just and lasting peace."
'No closer friends'
President Donald Trump - hosting the royal couple for four days - had earlier hailed Britain as America's closest ally as he welcomed Charles and Queen Camilla to the White House on a state visit overshadowed by tensions over the Iran conflict.
Speaking after a pomp-filled welcome on the South Lawn featuring a 21-gun salute, Mr Trump's tone was a world away from his recent jibes at British Prime Minister Keir Starmer for failing to join the US war against Tehran.
"In the centuries since we won our independence, Americans have had no closer friends than the British," Mr Trump said during a ceremonial reception.
Using a phrase popularised by Winston Churchill, he hailed the "special relationship" and praised Britain's military, saying the two countries had "fought better together" than any others.
Cannons rang out while a military band played the British and US national anthems, before Charles shook hands with top Trump administration officials and inspected troops on the lawn with the president.
A band of soldiers dressed in uniforms from the US Revolutionary War then marched past, playing fife and drums.
Afterward, four US jets roared over the White House in a noisy flypast as Mr Trump, Charles, Camilla and First Lady Melania Trump watched.
'Beautiful British day'
A long-term fan of the British royals, Mr Trump appeared in a jovial mood on a rainy Washington morning as he looked to the sky and quipped: "What a beautiful British day this is."
The 79-year-old president even joked about how his late mother "had a crush on Charles", who is now 77.
Charles shook hands with top Trump administration officials, including Vice President JD Vance and Secretary of State Marco Rubio.
The king and the president - who received his own state visit to Britain last September - inspected troops from different branches of the US armed forces.
As the ceremony unfolded, construction noise could be heard from the site of the huge $400 million ballroom that Mr Trump is building at the White House.
Tight security
Security has been tight for the visit, which comes just days after a shooting at a White House Correspondents Dinner attended by Mr Trump.
The first day of the trip featured a more informal welcome, with the Trumps treating Charles and Camilla to tea and cakes in the White House before showing them beehives on the famed lawn.
But the second day featured the most public-facing moment, when Charles became the first British monarch to address Congress since his mother, Queen Elizabeth II, in 1991.
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The long-planned visit has unfolded against tensions over the US-Israeli war on Iran, after Mr Trump repeatedly criticised Britain for declining to support the offensive, and after an internal Pentagon email suggested Washington could review its support for Britain's claim to the Falkland Islands.
Mr Trump has repeatedly lambasted British Prime Minister Keir Starmer over his war opposition, alongside the country's immigration and energy policies.
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— The White House (@WhiteHouse) April 28, 2026
The British government hopes the visit will shore up the transatlantic relationship by appealing to Mr Trump, a vocal admirer of the British royal family who often calls Charles a "great man".
Charles will also reference the shooting at the White House Correspondents' Association dinner on Saturday.
Tomorrow, the royals will be in New York City to commemorate those killed in the attacks of 11 September 2001, and the trip concludes in Virginia on Thursday with the king meeting people involved in conservation, reflecting his long-standing environmental advocacy.
He will then travel to Bermuda.
US only has 'special relationship' with Israel, says UK envoy to Washington
Israel, rather than the UK, is the country that enjoys a "special relationship" with the United States, Britain's ambassador to Washington recently remarked, according to a Financial Times report.
Christian Turner's comments have come to light at an awkward moment for US-UK ties, with King Charles III visiting US President Donald Trump in Washington.
Speaking to British students visiting Washington in mid-February, the ambassador expressed his dislike of the phrase "special relationship", typically used to describe the British-American alliance, according to the FT.
Mr Turner - who was appointed in December 2025 to replace Peter Mandelson after he was sacked over his ties to the late convicted US sex criminal Jeffrey Epstein - reportedly told the students he found the term "quite nostalgic" and "backwards-looking".
"I think there is probably one country that has a special relationship with the United States - and that is probably Israel," Mr Turner added.
When contacted by AFP, the UK foreign ministry called the remarks "private, informal comments made to a group of UK sixth-form students visiting the US in early February".
"They are certainly not any reflection of the UK government's position," the Foreign Office added.
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