Not even Brown can claim that on his blurb. "I certainly expect there will be a backlash, " the author, Kathleen McGowan . . . a former editor of the Irish News . . . said. "But I have the support of my family and friends and that's what I draw from."

McGowan's story of religious intrigue, The Expected One, is being published by Simon and Schuster, which paid a seven-figure sum for the book. The rights have been sold in more than 20 different languages while the initial print run in the US is a cool 250,000. The novel goes on sale in Ireland next month.

Digby Hallsby, a publicist with Simon and Schuster's UK division, said McGowan had been working on the book since 1989 and thus predated Brown's efforts. Asked how a publisher could authenticate the author's claim about her heritage, he said: "It's impossible to verify. It's all to do with a matter of faith. She makes a very convincing argument."

McGowan's claim to be descended from a child of Mary and Jesus is contained within an afterword in what she says is a partly-autobiographical novel. In an interview with USA Today she said she was unable to reveal the proof of her heritage but said she had traced it to an ancient French lineage that claimed to trace its roots to Jesus and Mary Magdalene.

McGowan, a married motherof-three who lives in Los Angeles, also said she experienced a vision of Mary Magdalene while on a visit to Jerusalem, an episode also experienced by the book's main character. Almost as outlandish as her claim is the fact that she has been taken seriously by Simon and Schuster, one of the book world's most respected publishers.

Legend has long linked Mary Magdalene with southern France and in the middle ages remains purported to be her relics were kept at the abbey of Vezelay in Burgundy. A rival tradition held that her remains were kept in Provence.

Both are based on the unproven belief . . . perhaps first written in a 12th century text . . . that she fled to France with Lazarus to avoid persecution after Jesus's death. Her feast day was yesterday . . . 22 July . . .

and remains observed by some to this day.

But academics are very sceptical about claims that Mary Magdalene travelled to France or that she and Jesus had a child. Bart Ehrman, chair of the department of religious studies at the University of North Carolina and author of Peter, Paul and Mary Magdalene: The Followers of Jesus in History and Legend, said:

"You can survey anyone who is a scholar of early Christianity and they will tell you the same thing . . . it's completely bogus. There are no records. We have no account of Mary Magdalene even going to France until the middle ages."

But McGowan remains adamant.

She says she cannot reveal the information she has about her roots but she stands by her story of experiencing her vision of Mary Magdalene. Furthermore, she says, she knew from then on that her life would be different. "It was so real and so powerful, " she said. "It was the moment I knew I would never be able to turn back, when I knew what I was seeing was real and it was true and I was being shown it for a reason."

And for those who like this sort of thing, there is plenty more where this came from: McGowan's novel is the first part of a trilogy.