Image caption His churchyard grave in Hertfordshire

From feral child to "human pet" at court in Georgian England, Peter the Wild Boy caused a sensation. And new analysis of his portraits may have solved the mystery of his unusual characteristics.

No-one knows if his name was really Peter - he couldn't talk. Nor did he walk, preferring to scamper on all fours, picking the pockets of courtiers and stealing kisses.

Peter had been found living alone and naked in a German forest in 1725, presumably abandoned by parents who struggled to cope.

The following year - aged about 12 - he was brought to London by George I where he became a "human pet" at Kensington Palace.

There was much fanciful speculation that he had been raised by wolves - or perhaps bears - and this was why he ate with his hands, disliked wearing clothes and could not be taught to speak, says Lucy Worsley, curator of Historic Royal Palaces.

"At the time, people assumed Peter acted the way he did because he was a wild child. They didn't suspect that something else could have been afflicting him."

She initially assumed autism, but found more clues in this portrait of Peter, by court painter William Kent, that hangs in Kensington Palace.

New analysis of this portrait suggests Peter had a rare genetic condition known as Pitt-Hopkins Syndrome, indicated by:

His short stature Lustrous mop of thick curly hair Hooded eyelids Cupid's bow mouth, with a pronounced curve to the upper lip He disliked clothes, but was wrestled daily into a green suit Pictured holding acorns and oak leaves - symbolic of living wild in the woods - and some fingers on his left hand (not seen) were fused

At Worsley's request, Professor Phillip Beales, of the Institute of Child Health, plugged these characteristics into his database of conditions caused by chromosome abnormalities.

There is scarcely talk of anything else Satirist Jonathan Swift on the 'wild boy' craze

The closest match is Pitt-Hopkins, a genetic condition only identified in 1978, which has severe neurological effects, says Professor Beales. "It's severe learning difficulties, developmental difficulties and the inability to develop speech."

Contemporary accounts chime with his diagnosis, such as this description of Peter's first appearance at court:

"The wild boy played with a glove of Caroline's [the Princess of Wales], grew fascinated by a pocket watch that struck the hours and, as was usual with him, attempted some mild pickpocketing. Furthermore, rumour spread that he had, in breach of all civilised decorum, seized the Lord Chamberlain's staff and put his hat on before the king."

Age of Enlightenment 17th and 18th Century intellectual movement also known as Age of Reason

It was a time of exploration, scientific endeavour and hunger for a better - and more rational - understanding of the world

Key figures included Rousseau, Voltaire, Newton, Descartes, the English philosopher John Locke and Scottish geologist James Hutton More on the Enlightenment

Tales of feral children always fascinate, but Peter caused a sensation. It was the Age of Enlightenment, and he became a symbol in the debate about what it meant to be human.

"People were beginning to question established authority and religion. And they were interested in what distinguishes us from the animals," says Worsley.

"If he has no speech, does that mean he has no soul? Do human beings really have souls? He raised lots of philosophical questions."

A waxwork figure was exhibited in the Strand, and noted authors - Jonathan Swift and Daniel Defoe among them - penned pamphlets about the wild boy.

But attempts to civilise him came to naught.

Image caption Peter's collar, so he could be returned home if lost

The king invited him to dine, but was horrified by his lack of table manners. The court doctor tried and failed to teach him to speak. Each day courtiers would wrestle him into a green velvet suit and each evening would try to persuade him into bed. Peter preferred to curl up on the floor in a corner of his room.

His novelty eventually waned, and the court paid for him to retire to a Hertfordshire farm.

"Many people like him in Georgian England would have been freaks in a circus, but he ended up in good hands. The farmers were fond of him, and had a collar made for him," says Worsley.

Pitt-Hopkins Syndrome Genetic condition only identified in 1978

Just 150 documented cases to date

Occurs in males and females equally

Many have no speech and slow motor development

Signs include Cupid's bow lips, flared nostrils, fused fingers and curly hair

Behaviour is always busy and moving

Generally of a happy demeanour

"It looks like the collar of a dog or a slave. But it was made with a kind thought, as when the wind blew in a certain direction, he would wander off. The inscription read: 'Peter the Wild Man of Hanover. Whoever will bring him to Mr Fenn at Berkhamsted shall be paid for their trouble.'"

When he died, the locals paid for a headstone. Even today, flowers are laid on his grave.

"He was a very gentle character and in some ways, more human than the rest of us," says Worsley. "His very existence exposed the shallow artifice of Georgian society as a bit of a sham."

National Treasures Live, which delves into Britain's historical sites and stories, is a five-part BBC One series starting Wednesday 10 August at 19:30