The moustache worn by Adolf Hitler is one of the most instantly recognisable and iconic features of any man in recorded history. However, according to new research after an essay was found written by one of the soldiers serving with Hitler in the First World War, this moustache was not his first preference. We can see in the picture above (left) that in 1914 he had a rather more common, thicker moustache.

The soldier, who happened to be a writer by trade, was serving with Hitler while he had great difficulty in the trenches making a tight enough seal with his respirator mask, soon afterwards Hitler was ordered to trim his moustache for the purpose of allowing the respirator fit correctly. Respirators were an important part of the German attire in the trenches due to consistent threat of British Mustard gas attack, The Wrap reports.

The surprising explanation is unearthed in a new biography of the writer Alexander Moritz Frey, who came to know Hitler when they were both lowly privates in a Bavarian infantry division. In a previously unpublished essay, Frey, who died in 1957, gave account of the first time he met Hitler in 1915, “a pale, tall man tumbled down into the cellar after the first shells of the daily evening attacks began to fall, fear and rage glowing in his eyes. At that time he looked so tall because he was so thin. A full moustache, which had to be trimmed later because of the new gas masks, covered the ugly slit of his mouth”

Stefan Ernsting, who wrote the new biography, uncovered Frey’s essay in archives found in the provincial German town of Marbach. Frey’s revelation proves disappointing for many historians, providing the first substantial challenge to the accepted wisdom on the subject, which has for the most part been that Hitler was simply following the fashion at the time.

Ironically, the changes in facial hair Hitler was forced to make to fit German respirators did not save him from being severely gassed and temporarily blinded at the time of a British attack in 1918.