Royal tours are unpredictable beasts. The planning is meticulous and dates back months, sometimes years, but there is always jeopardy.

King Charles III's visit to the Caribbean, which starts on Tuesday, takes him to three countries in nine days: the Bahamas, Guyana and finally Antigua and Barbuda for the Commonwealth Heads of Government Meeting (Chogm).

It also throws him directly into the heat of the debate over the payment of reparations - compensation from countries that took part in the slave trade - alongside questions of whether the King should be apologising for the UK's role in what he has previously described as an "appalling atrocity" that leaves an "indelible stain" on history.

"This is the biggest risk of his reign so far with so much just outside of his control," said author and historian Sir Anthony Seldon. "Questions about slavery, reparations and apologies mean the moral integrity of the monarchy is being questioned." The King will make three significant speeches during the Caribbean trip and will follow government advice not to issue an official apology for Britain's role in the transatlantic slave trade.

A senior royal aide said that the King would "not shy away from the darkest days of our past" but stressed that decisions over apologies and reparations were matters for government. The current Burnham administration, like those before it, will not pay reparations.

Buckingham Palace says that acknowledging the wrongs of the past will be built into the King's programme in all three countries.

But apologies, reparations, and republicanism are rich pickings for campaigners and protests are likely. This is the reality for the King and Buckingham Palace, and they are accepting of it.

Those who've worked on the planning of the trip view protests as part of the open debate in the region and security preparations include their possibility.

Lurking in the back of Royal Household minds will also be memories of the last tour by senior royals to the Caribbean in the early part of 2022.

Then, as the Duke and Duchess of Cambridge, William and Catherine found themselves facing criticism over the optics of the trip - images of the royal couple reaching out to touch the outstretched hands of Jamaican children through a wire fence looked clumsy. Engagements designed as tributes to past royal visits appeared outdated. And protests also caused the cancellation of a small part of the schedule. Everything will have been done to avoid those kinds of missteps on the 2026 Caribbean tour.

The leadership in the Bahamas, Guyana and Antigua and Barbuda will celebrate the King and his work in protecting rainforests, creating cultural ties and reinforcing relationships around trade, energy, and agriculture. But they do so against a backdrop of change. The leaders of all three countries have voiced their support for reparatory justice.

In Antigua and Barbuda and the Bahamas, where the King is head of state, the conversation about becoming a republic has significant support.

Elected officials in the former no longer have to pledge allegiance to the King ending a 40-year tradition of swearing loyalty to the monarch.

"He pulled off an extraordinary triumph with President Trump in his US visit earlier this year and stood up to him and put him in his place in a way that no leader has done - while not incurring his wrath," said Sir Anthony. "If he can deal with the delicate nature of this trip for him personally, for the British monarchy, and the future of the Commonwealth, it could be an enormous success." Timing also matters for royal tours. This Caribbean tour has to cut through a sea of royal distractions.

The King has spent much of the past three months in Scotland, where he is based over the summer. It should have been a quieter time in the royal calendar, but it has been quite the opposite.

The surprise return of the Duke and Duchess of Sussex to the UK has been noisy. The level of coverage Harry and Meghan get is unsettling and, at times, irritating for the Royal Family. The King's youngest son has not yet seen his father in person, but they are said to have talked.

Then enter Earl Spencer, the King's former brother-in-law, with his memoir, Swan Song, criticising the King's response to the death of Diana, Princess of Wales. It triggered a strong pushback from the Palace.

And in recent days, the serious claims made about Meghan's father, Thomas Markle, have drawn his daughter into a complex tale involving global police forces, sexual abuse allegations and further family trauma. An impactful and successful Caribbean tour is a chance to switch focus.

But if royal stories back home are running hot, it can be hard to focus minds on the King's engagements over four thousand miles (6,437km) away.

Former Foreign Secretary David Lammy, who has strong family ties to the Caribbean, has accompanied the King on a number of trips outside the UK.

"He is our head of state. He is amongst some of the most recognisable figures in the world. For a small country like Guyana, the validation of a state visit is huge," said the Tottenham MP whose father came to the UK from what was then British Guiana and who also has relatives in Antigua and Barbuda. "My mother would forever recall the Queen's visit in 1996." But there was also a recognition of that royal trip jeopardy.

"Knowing Guyana, Antigua and Barbuda as well as I do, he will be overwhelmingly received positively," Lammy said. "But these are lively democracies in which of course there will be some dissent."

A transatlantic flight, three countries over nine days and about 36 separate engagements when you're closing in on your 78th birthday is an intense schedule. It is also a reminder that the King is still dealing with a cancer diagnosis and having regular treatment. Buckingham Palace has reiterated its position that he is on a "positive trajectory".

Queen Camilla will only accompany the King on the Antigua and Barbuda leg of the visit for Chogm and a number of other engagements, including some around her own areas of interest – literacy and supporting efforts to end violence against women and girls.

The Queen, who will be 80 next July, is known to find the pace and hot conditions of some royal tours gruelling. This is a trip that comes with potential pitfalls but also the possibility of great reward for the King.

"The King can be an extraordinarily empathetic and in tune figure," Sir Anthony said. "He could play a blinder here."