The 10-month-old deer was born in captivity at the Centre of Natural Sciences, a nature reserve near Prato.
The 'unicorn' photographed in Tuscany, Italy
While single-horned deers have been spotted before, this particular buck has a uniquely central horn, thought to be the result of a genetic flaw.
"This is a demonstration that the fabled unicorn, which we all know from icons and legends, probably was not just a fantasy.
"It was probably an animal like this one, with a natural anomaly," said Gilberto Tozzi, the director of the centre.
Mr Tozzi added that the twin of the buck has two horns.
The mother of the two deer was brought to the park several years ago after being hit by a car in the Apennine mountains.
The mythical unicorn was thought to have healing powers and was generally depicted as a horse with the cloven hooves of a goat or deer.
The earliest mention of the beast was by the Greek historian Herodotus in the 5th century BC.
In one notebook, Leonardo Da Vinci suggested unicorns could be captured using a virgin as bait.