It was the feature that made him instantly recognisable.

Adolf Hitler's toothbrush moustache was as much his hallmark as a swastika and his side-parting hair style.

Now the story of how the dictator went from having an elaborate handlebar moustache to the style he is forever associated with has been told in Emmy-nominated series The World Wars.

The series produced by History Channel reveals that Adolf Hitler got his infamous toothbrush moustache after he had to trim his handlebar style to allow his gas mask to properly seal during the First World War.

The three-part series starts with a First World War soldier discovering that his handlebar moustache, complete with twisted ends, is preventing his gas mask from sealing tightly during a gas attack in a trench.

The soldier, revealed to be a young Adolf Hitler, is then shown trimming the facial hair into a neat square, creating the infamous style.

Stephen David, the series' executive producer, said while making the programme, his research team had learned how Hitler favoured a longer moustache prior to the outbreak of the First World War.

After the conflict ended in 1918, Hitler kept the moustache, still preferring the trimmed style as he rose to power in Germany in the early 1930s, and it soon became one of his most identifiable features.

David said, "I think in actuality after World War I that was a fashion, and a lot of people did that. Between World War I and World War II, that was a fashion that a lot of people had. And being that Hitler had it, he kind of killed that fashion".

Although popular between the wars, when it was sported by comedians Charlie Chaplin and Oliver Hardy, the toothbrush moustache fell out of favour after the Second World War due to its strong association with Hitler.