Video report by ITV News Royal Editor Chris Ship
Ever since Fidel Castro rolled into Havana in January 1959 and put his country on a collision course with the USA, no member of the British Royal Family has set foot in Cuba.
They’ve been to the Caribbean, many times, just as Prince Charles and the Duchess of Cornwall have done this week, but Cuba has always been off limits.
It’s 50 years since Castro’s Revolution, and for the first time Charles and Camilla stepped where no Royal has stepped before.
As the couple descended the stairs from the RAF plane at Havana airport and stepped onto Cuban soil, history was made.
This is a big deal, because, for five decades, British foreign policy has always sided with that of its closest ally, the United States.
In all that time, British prime ministers have been unable to visit, nor could any member of the Royal Family, even though they have travelled extensively in the Caribbean.
This week, for example, Charles and Camilla have toured five Realms - islands where the Queen remains the Head of State.
Cuba is another Caribbean island nation - but it could not be more different.
Fidel Castro might be dead, and his brother Raúl might have handed the presidency to a non-Castro for the first time - but Cuba remains a one-party state, controlled by the country’s Communist Party.
The diplomatic thaw between Britain and Cuba has been underway for some years now, but that process took a significant step last November when the current, President Miguel Díaz-Canel, who took over from Raúl Castro in April 2018, met Prince Charles at Clarence House.
A note on the Court Circular, the official record of engagements for members of the Royal Family simply stated: "The President of the Republic of Cuba called upon The Prince of Wales at Clarence House."
That meeting, described by officials as "warm", paved the way for this historic royal visit.
In a statement released on Sunday, Clarence House said both Charles and Camilla "are looking forward to experiencing the culture and meeting the people of Cuba".
Prince Charles and President Díaz-Canel will meet again on Monday in Havana.
Officially, there are "no plans" for the Prince to meet Raúl Castro - although aides in the Prince’s office say they can’t rule out Castro being at one of the events over the next three days.
Fidel Castro died in 2016, aged 90 - having survived dozens of attempts by the CIA to assassinate him.
The UK wants to have better diplomatic and trade ties with Cuba and we were following the path set by President Obama when he decided to reset US relations with Cuba and visited the country in 2016.
The US embassy in Havana had re-opened some months earlier.
However, under Donald Trump, that diplomatic thaw has begun to re-freeze.
A Trump supporting Senator from Florida had urged the Prince to cancel the trip.
Senator Rick Scott said: "A trip of this magnitude by the Crown provides unwarranted legitimacy to a dictatorship with a decades-long history of persecuting and imprisoning its defectors and repressing its people."
But the Foreign Office in London wants to have an open dialogue with Cuba and diplomats say they will continue to disagree over fundamental issues such as human rights and democracy.
But, as with other regimes, the view in the British government is those disagreements are better made when there is some dialogue between two countries - rather than none at all.
Prince Charles' visit paves the way for those UK-Cuba relations to make a significant step forward.
Being able to dispatch the Royal Family in this way - and Prince Charles is the most senior travelling member of the Family these days - is part of the government's arsenal of "soft" diplomatic power.
And this is why the royal arrival in Havana has marked a moment in British history.