The year 1911 was one of Liverpool's most turbulent. Tension among the city's seamen was to spill over into a general transport strike that would paralyse the "Second Port of the Empire" for 72 days and bring hardship to the thousands of families dependent on the men's wages.

But for a young Irish woman living in a tiny flat at 102 Upper Stanhope Street in the Toxteth area, the times were good. Bridget Dowling had met the man of her dreams at a horse show in her native Dublin the previous year. With his handsome features, fashionable clothes, and handlebar moustache the young Austrian, called Alois, appeared every inch a man of the world.

Telling her he was a wealthy hotelier studying the industry in other parts of Europe, he swept the impressionable 17-year-old off her feet. "Everything he said was so new and interesting that even his broken English seemed charming," she later recalled.

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But the course of Bridget's love was not to run smoothly. As the couple enjoyed trysts at Dublin's National Gallery and planned a future together, the girl's father, William, was growing concerned about the relationship. Not least because he had discovered his daughter's suitor was a waiter in the Shelbourne Hotel - a position he had been sent to by a London employment agency.

Pre-empting their disapproval, Bridget and her boyfriend eloped to London and were married on 3 June 1910. The wedding infuriated William Dowling who tried to have Alois arrested for kidnap. But by 1911, peace had broken out in the family and Bridget's father had made the sea journey to Liverpool to attend the baptism of his first grandchild. The child's name was William Patrick Hitler.

The boy was to grow up to be regarded as one of the most notorious scoundrels of the 20th century. A man who tried first to cosy up to, then to blackmail and to betray, before finally trying - for the rest of his lifetime - to conceal his relationship with his uncle, Adolf Hitler. Next year, British theatre audiences will have the opportunity to learn more about his extraordinary life when the New York playwright Mark Kassen brings his play Little Willy to the West End.

The one-hour show has already proved a hit with US audiences and critics. The New York Times described the character created by Kassen as "a parastic, failed careerist who had not one moral or political conviction that he wouldn't sell for a dime."

History has not been kind to William Hitler. Little is known of his early life growing up in Liverpool except that, like many around them, the family was poor. William's father ran a restaurant on Dale Street, a boarding house on Parliament Street and a hotel at Mount Pleasant. But his skills as a businessman were lacking and he was eventually made bankrupt.

Much attention has been focused on a visit to the family said to have been made at this time by his down-and-out half brother. In her memoirs, My Brother Adolf, Bridget said the future Führer stayed with the family between November 1912 and April 1913.

Back in Vienna, Hitler had been on the brink of destitution. By day he worked as a labourer, shovelling snow and beating carpets. At night he flopped down in a men's hostel. Worse was the threat of the draft and, claimed Bridget, he fled his native Austria for Britain to avoid it.

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Most contemporary historians have come to regard My Brother Adolf as a work of fiction and reject its depictions of cosy conversations around the kitchen stove with the future architect of European genocide. Among the claims made by Bridget is that she introduced Hitler to astrology - something which influenced many of the Reich's military strategies. She also claimed to have persuaded him to clip and restyle his handlebar moustache.

As his business fell apart, Alois deserted his family, returning to his native Germany where he sold razors. Faking his death, he entered a second, bigamous, marriage, a charge for which he was later prosecuted. Hitler Snr escaped jail only thanks to the intervention of his former wife who told the authorities she had legally separated from him.

Back in England things were going none too smoothly for his abandoned son either. With the rise of his uncle to power, and deteriorating relations between London and Berlin, William found the name Hitler a major impediment to his progress.

Jobless, he travelled to Germany thinking the family association could prove more beneficial. His uncle, by now Chancellor, found him a comfortable job with the Reichskreditbank, a position he occupied for much of the 1930s. The name Hitler helped open doors to the ambitious and gregarious William. Despite frustration at his low-ranking job, the young Hitler found himself invited to fashionable dinner parties and a sought-after guest at country house weekends where the Nazi elite gathered to enjoy the spoils of their complicity.

The family connection also proved an aphrodisiac and passport to the beds of many young women. His performance, however, was said to have left many of his "conquests" disappointed, according to the new play.

After repeated protestations, the Führer eventually secured a new position for his nephew as a salesman at the Opel car factory. The relationship was deteriorating. Cautious of being accused of nepotism, Hitler ranted: "I didn't become Chancellor for the benefit of my family ... No one is going to climb on my back." He began to refer to him in public as "my loathsome nephew".

Undeterred, William carried on exploiting his lineage. He travelled to Britain in 1937 where he gave an interview to the Daily Express declaring himself, in now heavily accented English, to be "the only legal descendant of the Hitler family" and even striking poses adopted by his uncle.

Storm clouds were gathering and the self-proclaimed leader of the master race decided it was time for his pushy relative to tie his colours firmly to the Nazi mast. But, fearing he might be trapped in Germany during the approaching war, William declined to renounce his British passport in return for a top job in the regime. He then tried to blackmail the Führer.

The details emerged years later at the Nuremberg trials. Hans Frank, the former Nazi lawyer responsible for millions of deaths while he was the Governor General of Poland, revealed how William had written to his uncle in the late 1930s threatening to expose the Hitlers' "unusual family history".

It was a veiled threat that he would confirm the long-held rumour that Hitler's paternal grandfather was, in fact, a Jewish merchant, Leopold Frankenberger, who had had an affair with his grandmother, Maria, during her time in service to the family in Graz.

It was a threat too far. William fled Germany but he received a frosty reception in his native Britain despite attempts to ingratiate himself with the public. His article published in Look magazine, entitled "Why I hate my Uncle", set the tone for the next few years.

As war began, William went on a lecture tour of the United States, regaling audiences with tales of his uncle's wickedness and the shortcomings of the Third Reich.

When America joined the war, Hitler Jnr wrote to President Roosevelt explaining that he had been refused permission to enlist in Britain and requesting to be allowed to join the US Army. "The British are an insular people and while they are kind and courteous, it is my impression, rightly or wrongly, that they could not in the long term feel overly cordial or sympathetic towards an individual bearing the name I do."

The letter was referred to the FBI which found no evidence of subversion and in 1944 cleared him to join the US Navy. A famous story reported in several newspapers at the time has William declaring his name to a recruiting officer who said: "Glad to see you Hitler. My name's Hess." It was the last time anyone was to hear of Hitler's nephew for decades.

In the meantime, his errant father, Alois, was captured and released by the victorious Allies. And the Hitlers' family home in Liverpool was destroyed in the last bombing raid of the war.

In 1998, the author David Gardner went in search of Hitler's Scouse nephew. His quest led him to the rural community of Patchogue on Long Island where he found that, after the war, Hitler had changed his name to William Stuart-Houston - strikingly close, say some critics, to that of the anti-semitic author whose work was favoured by the Nazis, Houston Stewart Chamberlain.

It emerged that Mr Stuart-Houston had married a German woman, Phyllis, in 1947. The couple had four children, three of whom survive today - Alexander, Louis and Brian. The eldest, Alexander, now a social worker, was given the middle name Adolf.

The family, who continued to speak German at home, were besieged by reporters following their "discovery". They claim that William, who had died in 1987 and is buried alongside his wife in the local Catholic church yard, had totally rejected his uncle's beliefs and had aggressively embraced the American dream.

His sons and his surviving wife have continued to defend their late father's reputation, declaring him a war hero - he was injured during military service - and extolling the work ethic with which he built up his blood-analysis laboratory from the family home. According to Gardner, the boys have never married or had children. Alexander has denied being party to a pact that the Hitler bloodline should die out with them.

But the last of the Hitlers' story is soon to be told. The youngest son, Brian, told one journalist: "Why should we talk to someone when we're writing our own book? We have a lawyer and an agent."