The actor John Hurt has just sufferedhis most painful experience since a newly hatched space monster burst out of his stomach in the first of the Alien films 30 years ago. He has been told that he is not Irish.
A family legend had maintained that Hurt's great-grandmother Emma Stafford was the illegitimate daughter of an aristocrat from County Sligo. She was, indeed, illegitimate, but the place whence she originated has a less glamorous ring than Sligo. She came from Croydon.
The actor, who lived in Ireland for years and identified strongly with the country, has discovered the disappointing truth after taking part in the BBC1 programme Who Do You Think You Are?, which will be broadcast tonight.
"I am not who I believed I was," he said. "That really upsets me. "As far as I was concerned I was Irish. My disappointment was that they had managed to prove that the one thing I thought I did have was Irish blood and I haven't got any."
The Hollywood star and his brother, Michael, a Benedictine monk from Glenstal Abbey in Ireland, were taken by the programme-makers to Westport House, home of the current Marquess of Sligo, in search of their supposed ancestry.
The Hurt brothers, whose father was an Anglican vicar in Derbyshire , did not know the name of the aristocrat whose descendants they aspired to be, but a historian hired by the programme reckoned that the prime suspect was Howe Peter Browne, second Marquess of Sligo, who was known to have had other illegitimate children.
Later in the programme Mr Hurt came across Emma's marriage certificate, which states her birthplace as Croydon. Her baptismal record, at Croydon parish church, gives her parents as Edward and Emma Stafford, with no hint of an Irish connection.
Then the story becomes foggy. There is a record of the young Emma Stafford attending a local boarding school, but no other evidence that her parents, Edward and Emma, existed.
It emerged that there is a scandalous secret in the Hurt family history, but not as glamorous as the one he was brought up to believe. That seems to have been invented to allow the family to claim a link to aristocracy.
Other actors have explored ancestral links with Ireland in the series. David Tennant, who plays Dr Who, learnt that his maternal grandmother, Nellie Blair, was born in Derry and met her husband, Archie Macleod, a footballer, after he moved from Scotland to play for Derry City.
Jeremy Ironslearnt that his grandmother's family were landowners from Cork. Barbara Windsor, of EastEnders, also had a family link to County Cork. Amanda Redman, of At Home with the Braithwaites, learnt that her maternal great-great-grandfather was born in County Wexford.
Other actors who could not claim to be Irish have at times worked hard to sound it on screen, though it is unlikely that any has matched the linguistic skill of "Richard the Spy", who infiltrated English forces fighting American rebels, led by George Washington.
Captured by the English, he escaped execution by masquerading as an Irishman, imitating the brogue so accurately that they were unable to convict him. He died a prisoner, claiming to the last that he was Irish.
Last year, the Dublin radio station Spin asked listeners to nominate the worst fake Irish accent to come out of Hollywood. The winner was Tom Cruise for his performance in Far and Away, followed by Brad Pitt in The Devil's Own, Richard Gere in Jackal and Julia Roberts in Michael Collins.