Peter Mandelson privately described a speech delivered by King Charles in Canada as "pretty political", according to newly released Government documents.
The remark appeared in the latest tranche of the Mandelson files - a collection of over 1,500 pages of emails, messages and official correspondence published on June 1.
Their publication followed a parliamentary order for greater transparency over Lord Mandelson's appointment as Britain's ambassador to Washington.
The exchange related to King Charles's historic visit to Ottawa on May 27, 2025, when the monarch opened the first session of Canada's 45th Parliament and delivered the Speech from the Throne on behalf of Prime Minister Mark Carney's newly elected Government.
It marked the first time a reigning monarch had delivered Canada's throne speech since Queen Elizabeth II did so in 1977.
In an email chain entitled "Canada: the King and the Speech from the Throne", Robert Tinline, Britain's High Commissioner to Canada, provided senior British officials with a detailed assessment of the speech and its reception.
Mr Tinline highlighted a line that received the only round of applause during the address: "As the anthem reminds us: The True North is indeed strong and free!"
He also pointed to passages stressing Canadian sovereignty, new international partnerships and a relationship with the United States based on "mutual respect" and "common interests".
In 2025, the monarch opened the first session of Canada's 45th Parliament and delivered the Speech from the Throne on behalf of Prime Minister Mark Carney's newly elected Government
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The email was circulated to several senior figures, including Ailsa Terry of No. 10, Caroline Hurndall and Labour chief strategist Morgan McSweeney.
Responding shortly after 1.30am UK time on May 28, Lord Mandelson wrote: "Thanks Rob for such a full read out.
"The chosen words all seem pretty political to me. I suspect they have had the desired effect in Canada but fortunately seem - so far - to have passed people by here in DC."
He added: "Hopefully we can move on and plan the President's state visit in a calm and successful way."
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The comments came at a particularly sensitive moment in relations between Canada and the United States
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The comments came at a particularly sensitive moment in relations between Canada and the United States.
In the months preceding the speech, US President Donald Trump had repeatedly suggested Canada could become America's "51st state", prompting widespread political backlash north of the border.
Prime Minister Carney invited the King to open Parliament in what many observers viewed as a symbolic demonstration of Canada's sovereignty and distinct constitutional identity.
While King Charles made no direct reference to President Trump, the speech's language attracted significant attention.
The monarch declared that Canadians could "give themselves far more than any foreign power on any continent can ever take away" and concluded by stating that Canada remained "strong and free".
Commentators widely interpreted the address as an implicit response to annexation rhetoric emanating from Washington.
Like the King's Speech at Westminster, Charles's Canadian address was written by the Government of the day and outlined its legislative priorities.
In this case, the text reflected the agenda of Mr Carney's Liberal administration rather than the King's personal views.
Lord Mandelson has repeatedly denied wrongdoing.
He has rejected allegations that he acted improperly in relation to Jeffrey Epstein and has denied any misconduct connected to his appointment process.