A mystery detainee who allegedly created a bogus identity as an English nobleman by assuming the name of a dead baby is actually an American who went missing from Florida more than 20 years ago, his relatives say.

The man being held in a jail in Kent, England, goes by the title of Earl of Buckingham, but really is an Orlando native named Charles Stopford, his father Charles and sister Rebecca Davis say in a documentary to be broadcast Sunday on Sky One television.

The relatives said they saw photos of the fake lord on the Internet along with a story in The Times this week and concluded he is Stopford.

"When I first saw his photo, I cried and I was excited because I was 100 percent positive it was him," Davis said in an excerpt of the documentary aired Saturday.

The elder Stopford said he has no idea why his son suddenly vanished from Florida in 1983.

But one of the man's brothers, Wesley, told The Times that the detainee had been convicted that same year of possessing explosives after he tried to blow up the car of his boss at a fast-food restaurant in Orlando. He was put on probation, but spent 60 days in jail after he violated the terms. Shortly after that, he disappeared.

"Charles always had an obsession with the English," his father said.

Davis said she had believed Stopford was simply traveling around Europe all these years.

"I remember him saying that he loved the thought of traveling. He wanted to travel Europe," she said.

British media have dubbed the man "The Real Jackal" -- an allusion to Frederick Forsythe's novel "The Day of the Jackal," which made famous the trick of using information from a baby's tombstone to create an identity.

In this case, the detainee was arrested in January 2005 as he tried to enter Dover, England, from Calais, France, across the English Channel. Police ran a passport check and saw that the person with his name was supposed to be dead.

He is alleged to have taken the name of Christopher Buckingham, who died in 1963 at the age of 8 months, and used it to obtain documents to live as a British subject.

For the past decade he has been calling himself the Earl of Buckingham, a title that has been extinct for more than 300 years.

The man served nine months in prison over the false passport incident. But after completing the sentence, he has remained in jail because he refuses to reveal his true identity.

"As far as we are concerned, he still claims to be Christopher Buckingham," Kent police spokeswoman Kelly Betts said.

The man apparently speaks with a perfect British accent, she added.

He has two English children by a woman from whom he is now divorced, and all three are said to be stupefied by news that he is not the man they thought he was, the Times said.

The newspaper said police in Kent have sent fingerprint and DNA samples to the United States to try to determine the man's identity.

Betts said she could not confirm the DNA and fingerprint report, but said British authorities were working with American embassy officials to determine if the man really is Stopford. "We are following up a number of leads to find out who he is," she said.