AN American sex offender posed as a fictional aristocrat from the North-East of England in an elaborate scam to con schoolchildren.

Joshua Gardner convinced pupils in the US state of Minnesota that he was the Duke of Cleveland and 27th in line to the British throne.

The 22-year-old faked a British accent, handed out business cards featuring a crest with a lion and unicorn, and told the students that he lived in a castle and was friends with Prince Harry.

But Gardner, from Austin, Minnesota, is now behind bars after a reporter from a school newspaper exposed him as a sex offender in breach of parole.

Gardner took on the persona of Caspian James Crichton-Stuart IV, the fifth Duke of Cleveland - claiming that he was in the US for ear surgery - on three separate trips to Stillwater Area High School, in Minnesota.

He told students that he was 17 years old and also demanded to be called "your grace".

However, the school's newspaper, the Pony Express, discovered his true identity.

In real life, Gardner was convicted in 2003 for sexual contact with a 14-year-old girl and last week he was jailed for breaching his bail conditions.

He was caught out when the Pony Express editor-in-chief, Matt Murphy, noticed he had misspelt the name of his castle and the British Consulate told him the Duke of Cleveland did not exist.

Mr Murphy said: "He said that he was looking at coming to the school for next year. Why would a member of the Royal family come to Minnesota for school?"

Speaking from jail, Gardner said: "Becoming Caspian, I was given respect. And people don't look at you in that way that they would look at a sex offender.

"I still don't understand how they found out. I must have been good enough for them to believe me for so long."

Gardner,who said he made up the persona last November, out of boredom, is suspected of illegal sexual contact with a student. He faces a maximum sentence of 21 months for parole violations.

* The fourth and last Duke of Cleveland, who lived in Raby Castle, Staindrop, County Durham, died in 1891. The castle is now owned by Lord Barnard, a distant descendant.