King Charles III is to speak with “unflinching honesty” and “sincere sorrow” on the lasting pain of the transatlantic slave trade, during the final leg of his Caribbean tour in Antigua, Buckingham Palace has said.

The King will address Commonwealth leaders on Tuesday in a speech which will touch on the issue.

Prime Minister Andy Burnham said earlier he was “open” to the possibility of the UK formally apologising for its role in slavery – a change in the government’s stance.

The Palace was reportedly told in advance of Burnham’s comments in an opinion piece on Friday night, and the King has not changed his speech in light of them.

The British government has never formally apologised for slavery or offered to pay reparations.

Burnham has stuck to his predecessors’ policy and stopped short of offering any consideration of reparation payments.

Conservative Party leader Kemi Badenoch described “endless talk about apologies” as a “distraction” from solving current problems.

She told BBC Sunday with Laura Kuenssberg: “The transatlantic slave trade happened centuries ago. It is time for the Commonwealth to start looking forwards, not endlessly backwards.”

The King will speak at the Commonwealth Heads of Government Meeting (CHOGM).

He “will not shy away from confronting the most shameful aspects of the past during this visit”, a Palace spokesperson said.

“You may therefore expect him to address them in his speech with unflinching honesty, sincere sorrow, and respect for the wider discussions that will be taking place between relevant governments on this issue at CHOGM and beyond.”

When asked about the King’s reaction to the prime minister’s comments, the spokesperson said it would “not be appropriate” for the King to address matters of policy relating to “the UK government’s position”.

The Caribbean tour has again thrust King Charles into the difficult debates over the UK’s colonial legacy in the region.

On his first stop in the Bahamas, the King delivered a speech where he spoke of the “suffering of the past”.

In Guyana, he visited the site of a Slave Rebellion where hundreds of enslaved people were killed.

Buckingham Palace said the visit was a chance for the King to learn more about the history of slavery and resistance. His engagements have also covered the environment, opportunities for young people and trade relationships with the UK.

Royal sources have stressed that decisions about an apology are a matter for government, not the Palace.

“His Majesty is well practised on the diplomatic tightrope,” a Royal aide said. “He is up for challenging visits with complex issues and relationships in play. He sees it as his role to ‘bat for Britain’, the Realms and wider Commonwealth.”

In a piece for the Guardian published on Friday night, Burnham described the transatlantic slave trade as a “brutal and barbaric violation”, and that Britain “must face up to the past”.

King Charles will welcome his pledge in the article to strengthen the Commonwealth as an organisation, which he views as a powerful vehicle for change.

The King will deliver the opening speech at CHOGM, which brings together leaders from those 56 states every two years in a different part of the Commonwealth.

Each biennial meeting has a theme, and this year’s is officially called Accelerating Partnerships and Investment for a Prosperous Commonwealth.

Queen Camilla is with the King in Antigua, and as the couple attended a church service on Sunday morning ahead of celebrations to mark Independence Day on the island, it reminded everyone of the week’s intended focus.

Bishop of North Eastern Caribbean and Aruba, Ernest Flemming, told the congregation that the Commonwealth’s “prosperity” must be “shared prosperity”.

“True partnership requires mutual respect; it requires listening; it requires fairness.”

A Buckingham Palace spokesperson said: “Institutions are under strain across the globe. The Commonwealth has scale and breadth, but is also small enough for leaders to know each other and co-operate together.”

The King, they said, “contributes ideas and encouragement on a wide range of issues, delivering practical results which help improve the lives of millions”.

King Charles to address slavery in Antigua as PM says he is open to possible UK apology

The King has had a difficult few months, with developments surrounding his brother, Andrew Mountbatten-Windsor, and the publication of a book by his former brother-in-law, Earl Spencer.

In addition, his son, the Duke of Sussex, made a surprise move back to the UK in August with his wife, Meghan, and their two children.

Asked whether the King was confident his approach to family matters had been right in terms of public attitudes towards the institution, the response was concise. “Yes,” a senior aide told the BBC. “That is why he takes the actions he does – and has done.”

On serious allegations about Meghan’s father, Thomas Markle, the Palace did not want to comment publicly: “We wouldn’t comment on private family matters.”

The King is also still being treated for cancer. He was diagnosed in early 2024, and the Palace says he remains on a “positive trajectory”.

In hot, humid conditions, he will soon celebrate his 78th birthday and will have carried out about 36 engagements by the end of this nine-day Caribbean tour.