Mystery has always surrounded the death of King Boris III of Bulgaria, who died in 1943 at the height of World War II following a heroic defence of his Jewish subjects.
As part of celebrations to mark the anniversary, Boris's grandson Prince Kyril - partner of British businesswoman Katharine Butler - tells ¡HOLA! the whole fascinating tale, which has now been turned into a play, opening in London on 26 September.
It's said that your grandfather stood up to Hitler to save 50,000 Bulgarian Jews from deportation. You must be very proud of him.
"Yes. It was really a joint achievement by him, as head of state, together with the head of the Orthodox Church and groups like doctors and lawyers, who formed a united front to defend them from the Nazis."
But it was your grandfather who stood up to Hitler during a meeting at his own home?
"Well, after months of delays and difficulties in deporting the Jews, Hitler summoned King Boris in August 1943 to demand an explanation. The Germans were also unhappy that Bulgarian troops were not fighting with them on the Eastern Front. So Hitler confronted King Boris, face to face, without anyone else present."
The aim clearly being to frighten him.
"Exactly. The people outside the office could hear the Fuhrer shouting like a madman, for 45 minutes. This was after the Nazis had lost the Battle of Stalingrad, and the war was starting to go badly for them, so for him to get so worked up over this shows how crazy and sick he was."
But your grandfather wouldn't give in to him?
"No, and then, a few days after returning from Berlin, Boris died... despite having previously been perfectly fit and healthy. He paid for his actions with his life.
"My grandmother refused to have an autopsy done, so we don't know for sure what happened. However three doctors who examined the King, one of them sent by the Germans, all said that the symptoms, including a skin reaction, pointed to some kind of poison, that it was the only explanation."
The events have been turned into a play, The Brief Life and Mysterious Death of Boris III, King of Bulgaria. Have you been involved in the project?
"I've supported it in every way I can and now, following its debut at the Edinburgh Festival it's been booked by London's Arcola Theatre, where it will run for a month starting on 26 September."
What did your partner Katharine think when she saw it performed?
"She was impressed, like the audience, who have found it interesting and beautiful.
"I'm so lucky to have Katharine; we have a lot in common and really enjoy being together."
Has your father, King Simeon II, told you any other wartime anecdotes about Boris?
"No. He was only a little boy of six when my grandfather died."
Bulgaria has been a republic since 1946, but your family maintain close links with the country, where your father has even served as Prime Minister.
"Yes. We were recently able to hold a commemoration service for my grandfather at Rila Monastery, which is a spectacular place. The government even provided a guard of honour dressed in the uniform of the monarchical era. For my father, it was a total flashback to those days when he lost his father, so very emotional.
"Bulgaria is getting a bit more in touch now with its pre-communist history. And a lot of people feel affection for Boris, who touched the lives of so many."
Words by Antonio Dieguez.
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