Alexander the Great may have been killed by toxic wine made from a poisonous but harmless-looking plant, scientists have claimed.

The mystery of why the Greek King of Macedon, ruler of the largest empire in the ancient world, died at just 32 has baffled historians and scientists for over 2000 years.

Some argue that he passed due to natural causes while others believe he was secretly murdered using poison at a celebratory banquet.

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His death in 323BCE came at the palace of Nebuchadnezzar II in Babylon after he developed a fever and soon became unable to speak and walk. He was ill for 12 days.

Dr Leo Schep, a toxicologist from New Zealand’s National Poisons Centre says it is impossible that poisons such as arsenic were to blame - as cited in some theories - as death would have come too fast.

Instead, in his new research, Dr Schep argues that the most likely culprit was Veratrum album, a poisonous plant from the lily family also known as white or false hellebore.

Often fermented by the Greeks as a herbal treatment for inducing vomiting, importantly, it could account for the 12 days it took for the leader to die.

It would also match an account of Alexander the Great’s death written by ancient Greek historian Diodorus, who said he was struck with pain after drinking a large bowl of unmixed wine in honour of Hercules.

“Veratrum poisoning is heralded by the sudden onset of epigastric and substernal pain, which may also be accompanied by nausea and vomiting, followed by bradycardia and hypotension with severe muscular weakness. Alexander suffered similar features for the duration of his illness,” the research, printed in the medical journal Clinical Toxicology says.

Dr Schep has been working on the mystery for over 10 years after he was approached by a team for a BBC documentary in 2003.

“They asked me to look into it for them and I said, 'Oh yeah, I'll give it a go, I like a challenge' - thinking I wasn't going to find anything. And to my utter surprise, and their surprise, we found something that could fit the bill,” he told The New Zealand Herald.

Dr Shep does however caution that despite his theory, the actual cause of death cannot be proven: “We'll never know really,” he says.