Addressing the United States Congress this week, King Charles III made a cameo appearance in his role as Australia's monarch: “We have agreed (to) the most ambitious submarine program in history – AUKUS – in partnership with Australia, a country of which I am also immensely proud to serve as Sovereign.”
The idea that a British monarch would switch crowns mid-speech and tout a key Australian strategic objective while on a state visit to the United States would have seemed far-fetched only two years ago when Joe Biden was president. But since Donald Trump took office a second time, Charles’ role as sovereign has taken on newfound utility for Commonwealth realms that are also traditional allies of the United States.
Canada was the first beneficiary of Charles’ diplomatic power with Trump. The US President began his second term in January 2025 threatening Canada with annexation, referring repeatedly to the country as America’s “51st state” and then prime minister Justin Trudeau as “governor”. All this was followed by Trump imposing tariffs on many Canadian goods.
In response, on 3 March 2025, Trudeau sought and received an audience with Charles at Sandringham House. Following the meeting, Trudeau released a statement stating that the two had discussed “matters of importance to Canadians – including, above all, Canada’s sovereign and independent future”. A day later, Charles was photographed wearing Canadian medals on his military uniform while inspecting the aircraft carrier HMS Prince of Wales before a deployment to the Indo-Pacific. The symbolism was hard to miss.
Charles’ public interventions boosted popular support for the monarchy in Canada. Two days before he opened the Canadian parliament on 27 May 2025 – a rarity for Canada’s sovereign – a poll found that 45% of Canadians said Canada should remain a constitutional monarchy, while 39% said they thought Canada should end its connection to the crown (15% said they did not know).
Though comparing opinion polls is a fraught business, Australian support for retaining a constitutional monarchy appears broadly in line with that in Canada. In November 2025, a poll found that 43% of Australians would support becoming a republic, while only 28% would rather Australia remain a monarchy (29% were undecided).
Given the relatively soft support for a republic and the well-documented difficulties of achieving constitutional change in Australia, including the failure of the Voice referendum in October 2023, the monarchy is likely to remain at the cornerstone of Australia’s constitution in the near-to-medium term at least.