It looks like it just walked out of a fairy tale, but this deer with a single, unicorn-like antler is the real thing.

Shot by a hunter in Celje, Slovenia (map), in August, the roe deer has an extremely rare type of antler deformity, likely caused by an injury early in the antlers' development. Such injuries are common in deer and often lead to antler abnormalities, including bizarrely shaped racks.

The abnormal antler on this Slovenian "unicorn" is so unusual that scientist Boštjan Pokorny, who verified the animal's authenticity, said he's never seen anything like it in nature.

"In this species, only males grow antlers, which are bilateral and usually symmetrical bone structures that appear from two antler pedicles, i.e. extensions of the skull," Pokorny, assistant director of the ecological research institute ERICo Velenje, said in an email.

"However, in the case of this very untypical and interesting buck, both pedicles, which should be separated, grew up together in one large pedicle."

Magic Antlers

Roe deer, the most abundant and widespread game species in Slovenia, are carefully managed by the government, which sets guidelines for how many animals can be hunted each year.

The hunter who shot the "unicorn" selected it for its advanced age and because it had just one antler. Any deer can lose an antler any number of ways, and a remaining antler is referred to as a "spike." However, from a distance, there was no way for the hunter to know that this animal had a rare deformity rather than a spike, according to Pokorny.

Though the Slovenian unicorn may not be a mythical beast, antlers—which are found in every deer species—are a little bit magic.

"The cells that actually make the antler grow, they're some of the most amazing cells known to man," said Kip Adams, certified wildlife biologist and director of education and outreach for the Quality Deer Management Association, based in the U.S. state of Georgia. In fact, antlers represent the most rapid bone formation known in mammals.

Antlers are made from bone and are typically grown and cast off in a yearly cycle, whereas horns (think of a bighorn sheep) are permanent and composed mostly of keratin—the same substance that makes up hair and fingernails. (Related: "Arabian 'Unicorn' Leaps Out of Near Extinction.")

Life Cycle of an Antler

In many deer species, longer periods of sunlight trigger a release of testosterone in the male deer's body, which in turn spurs antler growth. From spring to fall, the antlers are composed of soft, living tissue, mostly blood and nerves, and are covered by a fuzzy layer of skin often referred to as velvet. (See "Deer Antler Velvet—What Is It, How Does It Work?")

At this point, antlers are extremely sensitive and prone to injury, such as the one the unicorn deer might have suffered.

"If they get hit by a car or get kicked by another deer, well, that can cause abnormal growth for the rest of the year," said Adams.

As daylight and testosterone levels ebb in the fall, antlers mineralize and turn to bone.

When the seasonal cycle is complete, usually in winter, the deer's body begins to reabsorb some of the nutrients at the base of the antler. This weakens the area and allows for the antlers to pop off without injuring the animal. (Watch "Amazing Antlers.")

That's how it works for most deer species—the roe deer actually grows its antlers through the winter and spring and then casts them off in the autumn.

Healthy Unicorn

Pokorny said he doesn't believe the deer's defect affected its ability to thrive. For one, it had already reached an old age, and the animal's weight was above average when it was killed.

He also noted that roe deer are territorial, and mating success is based mostly on a male's age and body size. (Related: "Rare Saola, Dubbed 'Asian Unicorn,' Sighted for First Time in 21st Century.")

So unlike other deer species, the bizarre animal wouldn't have needed his antlers to square off against other males.

Even so, we're pretty sure that any rival would have been scared off by the sight of a unicorn.