Was King Boris III of Bulgaria poisoned by Hitler? Podcast explores mystery surrounding death of the monarch, 49, during WWII after he collapsed and was found with 'brown spots' on his body - as his children say he was killed

The sudden and suspicious death of King Boris III of Bulgaria in 1943 at the age of 49 has mystified historians for decades; and more than 80 years on, his family is still looking for answers. 

It was first reported that the Bulgarian monarch died of a heart attack but, 80 years on, journalist Becky Milligan alongside Boris’s children King Simeon II, 86, and Princess Marie Louise, 91, look into whether he was actually murdered in a podcast, The Butterfly King.

The podcast explores numerous theories into the sudden death of the King; including suggestions then-British Prime Minister Winston Churchill was behind his demise or that he was killed by his friend, Adolf Hitler, with whom he shared a complicated relationship. 

In August 1943, during a crucial turning point in the Second World War, Boris had a meeting with Hitler, which lasted eight hours and apparently went badly. Two weeks later, the king was dead.

Boris found himself in a difficult situation during the war and was faced with two choices: side with the Allies and face a German invasion; or side with Hitler and become complicit in mass murder.

King Boris III of Bulgaria, who ruled from 1918, died aged 49 in 1943 in suspicious circumstances, 80 years on, journalist Becky Milligan looked into his death in podcast The Butterfly King

In the days after Boris's 1943 meeting with Hitler, he appeared very ill and broke out in a rash and a high fever. He even started convulsing at his most unwell.

Two weeks after meeting with the German dictator, he was dead. 

Simeon, who was just six years old when his father died, said: 'To this day we can't really blame anybody or point our fingers at anybody, yet we have this ghastly suspicion that something was wrong.

'He was feeling sick, then his liver eventually didn't function and there was pneumonia. He lasted so long, from Monday to Sunday.'

Marie Louise, who was 10 when she lost her father, described the official line of his death being a heart attack as 'BS'.

Boris’s wife, Giovanna of Savoy, was on holiday with the children on the week of his death but bizarrely, she was never told her husband was seriously ill at home until just before his death.

Marie Louise said: 'My mother was convinced he was done in by somebody. It was wartime, there would have been many many people that would have been happy to get rid of him.'

Simeon added: 'The doctors kept everything a secret and this was one of the reasons that everybody suspected foul play.'

Speaking about finding out that their father was dead, the siblings claimed they had to piece it together themselves before they were officially told.

King Boris’s children King Simeon II, now 86, (second left) and Princess Marie Louise, now 91, (third left) also believe their father was killed

In August 1943, during a crucial turning point in the Second World War , Boris (left) had a meeting with Hitler (right), which lasted eight hours and apparently went badly. Two weeks later, the king was dead

Queen Margarita of Bulgaria (centre) and Princess Marie-Louise of Bulgaria (right)  attended the 80th Birthday of King Simeon (left) in 2017, Sofia

Marie Louise said: 'We drove into Sofia [capital of Bulgaria] and there were black flags hanging from the buildings and then I knew it.'

Simeon added: 'My father's aide came up to me and he addressed me as 'your majesty', not your highness which was the usual. That's when I suddenly realised, my God, he is addressing me like the King, i.e., my father has passed away.'

During the Holocaust, Boris remained a friend to Adolf Hitler as he rounded up Jews from across Europe and murdered them. In 1941, he signed a pact with Germany, Italy and Japan which meant he was siding against the Allies.

However, when it came to the Jewish population in his own nation of Bulgaria, the top-secret plan to deport them to Polish concentration camps was scuppered when the details were leaked. It is believed Boris signed an order to let the people go; thus disobeying Hitler's orders.

Although there are suggestions Boris and Hitler ended up at loggerheads, the Bulgarian King's children don't believe the Germans had their father killed, believing they had 'no motive'. 

Simeon: 'One thing that disturbs me, is when I see people not being objective, I like objectivity...there is nothing rational, we have no proof.' Marie Louise added: 'I am convinced it wasn't the Germans.'

Boris and Hitler were apparently close friends and to protect Bulgaria the King had signed a pact with Germany, Italy and Japan in March 1941 and he quickly became an enemy of the Allies, United Kingdom, United States, Soviet Union, and China (pictured at the 1936 Olympics in Berlin)

King Boris sitting with his wife Giovanna of Savoy and his children Marie Louise and Simeon in the garden of the Royal Palace in Sofia in September 1939

The marriage between King Boris III of Bulgaria and Princess Giovanna of Savoy in October 1930

Despite original reports that King Boris III had died of natural causes, the podcast uncovers a historical society document written 10 years after Boris died; claiming 'it was no natural death'. 

Instead it determined the monarch's cause of death was 'poison of Asiatic origin' - that is, a poison characteristic to an Asian nation. 

The emergence of the document suggested that laboratory tests had been carried out to determine what killed the King, but it had never been made public until now.

Boris's actions during the Second World War have long been criticised and debated, as he oversaw the deportation of 11,000 Jews from Macedonia (a territory which Bulgaria had recently recovered) to a concentration camp in Poland.

However, some question if Boris had enough power over this territory to stop the deportation at the time.

As Milligan followed the trail of poison, a brand-new suspect came into the frame; the Soviet secret services. One theory suggested that Boris was simply in the way of Stalin's Soviet Union, who occupied Bulgaria in 1944, one year after Boris' death.

Stalin dreamt of spreading communism across Eastern Europe to create a buffer of territory to protect the Soviet Union - and Bulgaria was sandwiched between Romania and Greece.

However British historian Tessa Dunlop wasn't convinced that Russia had anything to do with the King's murder and instead thought communists from within Bulgaria might be the culprits.

She said: 'I'm not saying that any of these individual parties couldn’t have been capable of it, this was the Second World War, it was the biggest period of mass murder known to human mankind ever, don't rule out the communists on the ground.'

The Bulgarian Communist Party had a fractured relationship with the King who had banned its existence in the 1930s - so it was certainly a group with an axe to grind.

The investigation into the King's death was thrown into a tailspin when a doctor who examined Boris' heart in an autopsy revealed he saw no signs of poison and declared that the monarch did indeed die of a heart attack.

Simeon said: 'The doctors kept everything a secret and this was one of the reasons that everybody suspected foul play' (Simeon pictured with his wife Queen Margarita in 2021) 

Former Prime Minister Simeon and Margarita attended a reception at Buckingham Palace for overseas guests ahead of the Coronation of King Charles III and Queen Camilla in 2023

Dr Deutschendorf, who died from Covid just before his interview with the podcast host, claimed the king died a 'natural death.'

Forensic pathologist Dr Stuart John Hamilton revealed that it is possible Boris could of been suffering with angina, which is chest pain caused by reduced blood flow to the heart, on the lead up to his death.

He claimed that he may have had a heart defect since birth which he didn't know about, however he added that, given his profession, it's important for him to consider the context of the death.

He said: 'I would never stand up in a court and say beyond all reasonable doubt this is a homicide, but there is too much to it for me to comfortably say, 'write it off, we never need to look at that again'. In my profession we don't like loose ends hanging there.'

Marie Louise is still convinced her father was murdered despite being aware of Dr Deutschendorf's findings.

She said: 'You can induce a heart attack, that is not an answer, there are many ways to bring someone to a heart attack.

'I am convinced something was put into his soup, he had dinner with somebody alone, an assistant who worked with him.'

Dr Hamilton added: 'Certainly there are substances that can mimic a heart attack, like cocaine, it causes the arteries of your heart to spasm or close. I'm not suggesting he was on cocaine, but I am thinking of things that can cause your arteries to spasm and stop the blood flowing through them.'

Dr Hamilton revealed he does think that 'something underhand has gone on' because he can't explain why Boris's body was covered in brown spots after his death - which is not indicative of a heart attack. 

Edwin Stevoff, who was the King's closest advisor, had a private dinner with him the night before he collapsed and that meal, which was mushroom soup, ended up being the King's last.

The next morning doctors noticed Boris' skin was covered in brown spots as if he had been poisoned.

Mushroom poisoning became popular in the 1930s and the Soviet Union actually had opened poison laboratories, where they had held tests on prisoners, and tried to create a toxin that would mimic a heart attack.

The Soviet Union and Russia have a history of using poisons against alleged traitors, most famously killing Alexander Litvinenko in 2006 with a radioactive cup of green tea.

Host Milligan concluded: 'I'm going to call it, after months of investigation, I believe King Boris was murdered by the Soviets. Boris's murder has the Soviets' hallmarks stamped all over it, they had the means, and with their embassy next to the palace the Soviets had plenty of opportunity to slip the poison into the King's food or drink.

'As for their motive, remember Stalin dreamed of spreading communism across Eastern Europe and Bulgaria was a vital foot hold for anyone trying to consolidate their power in the region, but there was a king in the way, a very popular king.

'And if it was the Soviets the plan worked because just one year after the king's death the red army marched into Sofia and the iron curtain swallowed up Bulgaria. I believe he was murdered by the Soviets or by the Bulgarian Communists with help from the Soviets.'

Marie Louise added: 'Who had the greatest advantage to get rid of him? The Soviet Union.'

Simeon said: 'There must have been foul play, he died in a strange way, the pathology itself is even strange though.'