As Britain publicly distances itself from President Donald Trump’s pressure campaign on Iran, King Charles III’s upcoming visit is shaping up to be more than a royal spectacle.
It could be Britain’s most important diplomatic tool to prevent growing policy rifts with Washington from deepening.
Mendoza said Charles could play a crucial role at a time when British Prime Minister Keir Starmer’s government and Trump appear increasingly divided over Iran, defense strategy and the future shape of the transatlantic alliance.
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The trip began in Washington, DC, where King Charles and Queen Camilla were greeted by President Donald Trump and Melania Trump for a private tea. (Anna Moneymaker/Getty Images)
“King Charles has the opportunity, through personal diplomacy, to create a new beginning with Donald Trump,” Mendoza said.
The British balancing act became clearer on Monday when Deputy Prime Minister Stephen Doughty publicly rejected US blockade tactics against Iran, while still backing Washington’s wider efforts to secure maritime traffic through the Strait of Hormuz.
“While Britain does not support the US blockade, it does support working with the United States and others to reopen the Strait of Hormuz,” Doughty said ahead of a UN Security Council meeting, according to The Associated Press, warning that Tehran should not be allowed to “hold the rest of the world hostage.”
The split underlines London’s efforts to support US security goals without fully endorsing Trump’s “economic rage” strategy, which aims to strangle Iran’s economic lifelines through aggressive maritime pressure.
That difference in policy has intensified the investigation into whether Charles’ visit now functions as a diplomatic pressure valve.
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King Charles III and Queen Camilla disembark from their plane at Joint Base Andrews, Maryland, on April 27, 2026, to begin their state visit to the United States to celebrate the 250th anniversary of the country’s independence. (Win McNamee/Getty Images)
Mendoza pointed to Queen Elizabeth II’s past interventions as evidence that the monarchy can sometimes succeed where elected leaders cannot.
He cited Elizabeth’s historic role in easing tensions with Ireland and described royal diplomacy as uniquely positioned to build trust on a personal level.
“People often wonder why the British monarchy still exists in the 21st century,” Mendoza said. “Here’s why.”
Yet Mendoza was careful not to exaggerate the king’s role.
Charles is unlikely to have a direct influence on specific policies toward Iran, NATO or military cooperation, he said. Instead, his greatest value lies in shaping what Mendoza called the “general mood music” around Trump’s willingness to engage.
“It’s more a matter of general mood music, which could make the president more receptive to interesting solutions,” Mendoza said.
That distinction could prove crucial.
Rather than forcing policy alignment, Charles could help maintain the broader strategic atmosphere necessary for Washington and London to function as close allies even if their elected governments disagree.
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Prince Charles and Camilla hosted President Donald Trump and first lady Melania Trump during a state visit in 2019. (Chris Jackson – WPA Pool/Getty Images)
This could be particularly important for Britain, as outside analysts warn that the ‘special relationship’ is under increasing structural pressure.
In an analysis published on Monday, Matthias Matthijs, senior fellow at the Council on Foreign Relations, argued that while the royal visit offers “spectacle and ritual”, it is unlikely to undo the deeper unraveling of ties between the US and Britain.
Matthijs pointed to Trump’s repeated criticism of Starmer over immigration, energy policy and Britain’s stance on the US-Israeli confrontation with Iran, suggesting Charles could now do much of the diplomatic “heavy lifting” needed to maintain British access to Trump.
Meanwhile, constitutional scholars in Britain have also raised concerns.
Francesca Jackson warned earlier in April at the British Constitutional Law Association that using the monarch as a diplomatic tool during periods of sharp political volatility could expose the Crown to political backlash or “potential embarrassment”, especially if Charles is seen as caught between Trump and Starmer.
That risk reflects the broader stakes.
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King Charles III and President Donald Trump inspect the Guard of Honor during the state visit to Windsor Castle in Windsor, England, September 17, 2025. (Anna Moneymaker/Getty Images)
If Trump embraces Charles while continuing to criticize Starmer, the visit could maintain royal rapport while underscoring political dysfunction, effectively creating a parallel diplomatic path between Washington and the British Crown.
But for now, Mendoza argues, the purpose of the monarchy is not governance but access to the king, who may still have a chance to prevent the relationship from breaking down beyond repair.
