In the middle years of the 1950s, my father earned a few pennies by tending to the gardens of Sean Ross Abbey in Roscrea, Co Tipperary. Run by Sisters of the Sacred Hearts of Jesus and Mary, it was a place where so-called "fallen women" were kept and to this day, he recalls the unmistakable sound of sobbing that could be discerned behind the grey stone walls.
There is a chance that one of the women he heard crying was Philomena Lee. Originally from Limerick, she became pregnant in 1952 and, on telling her appalled family, she was placed in the care of the nuns at Sean Ross.
Philomena was just 18 and like many unmarried expectant mothers at the time she was considered a moral degenerate in an Irish society that was ruled with an iron fist by Archbishop John Charles McQuaid.
Sean Ross was one of numerous church-run institutions set up to keep unmarried mothers out of sight and mind, and Philomena would spend three arduous years there in what, effectively, amounted to incarceration.
But that was nothing compared with the heartache she would suffer when, in 1955, her son Anthony was removed from her care by the nuns, and put up for adoption. She was not allowed to say goodbye to him, but managed to catch a glimpse of him being bundled into a black car and driven away.
She would never see her boy again, and much later learned he had been sold by the church to a childless couple in the US, who had travelled to Sean Ross to adopt two children that summer.
For almost 50 years, Philomena kept her secret close to her heart. The Mother Superior, Sister Barbara, had often warned her not to breathe a word about Anthony to anyone and, partly as a result of the deeply ingrained shame she had felt, Philomena kept her word. She had also been forced to sign a document that forbade her from ever attempting to make contact with the child she had carried for nine months and had raised for three years.
But then in Christmas 2004, Philomena – who had emigrated to England after being released from Roscrea in the late 1950s – finally told someone: her daughter, Jane.
And it was thanks to Jane that her mother's story would go on to reach a wide audience – first through the compelling 2009 book, The Lost Child of Philomena Lee, by the former BBC journalist and New Labour spin-doctor Martin Sixsmith, and now thanks to the forthcoming film, Philomena, which stars Judi Dench and Steve Coogan and is based on that book.
"The main aim of the book was to find out what had happened to Philomena's son," Sixsmith says. "Working with her on it became something of a therapeutic exercise for her."
It makes for unbearably sad reading. Thanks to Sixsmith's journalistic endeavours, Philomena was to learn that Anthony was adopted by a devout Catholic couple from St Louis. He grew up as Michael Hess and was a brilliant A-list student who excelled at cross-country running. He would go on to become a celebrated lawyer and strategist for the Republican Party in the US.
Just as Philomena had made several futile efforts to contact her son over the years, so too had Michael been thwarted in his attempts to meet his mother. Plea after plea to the nuns at Roscrea were rebuffed. "They just didn't want to know," Sixsmith says.
Michael's final attempt to find his mother was heart-rending. Having contracted HIV some years before, he flew to Ireland in 1993 and begged Sean Ross to help him find his mother before it was too late – but the nuns would not relent. He died two years later, never to know who his mother was or that she had been trying to reach him too.
"It was very upsetting for Philomena to find out what had happened," Sixsmith says, "and devastating to know that he had been looking for her too."
The film – which opened to rave reviews at the Venice Film Festival last weekend and is directed by the acclaimed Stephen Frears – will, Sixsmith believes, lay bare the ills of Catholic Church-run organisations in Ireland for much of the 20th Century to a large international audience.
"It's a fantastically moving film and Judi Dench gives a real sense of Philomena as she is, even if her Irish aspect is over-played a bit. Philomena has lived in Britain for most of her life."
In the film, Sixsmith is played by Steve Coogan, although he is at pains to point out that the performance is far removed from the actor's most famous creation, Alan Partridge.
"Steve co-wrote the script and felt there should be lighter, comedic moments to counteract some of the darker themes. But, trust me, this is a terribly sad film," says Sixsmith.
Meanwhile, Stephen Frears is insisting that the Vatican be made aware of Philomena's story – and those of hundreds, if not thousands, of other women like her. "I am very keen that the Pope should see it," he said.
Today, Philomena (80) takes comfort in her two adult children and the knowledge that thanks to Sixsmith's book, other children sold off by the church in the 1950s and 1960s have been inspired to make contact with their birth mothers.
The film – which will be released on November 1 – may well send other people in the direction of Sean Ross, which today is celebrated as one of the country's top schools for disabled children.
At least Michael Hess got to have one dream realised. On his last, futile, visit to Sean Ross he asked if he could be buried in the small graveyard in the grounds of the Abbey. It would, he hoped, let his mother know he had looked for her if she ever came back to Sean Ross. The nuns said they would allow his wish.
A simple headstone marks the spot today – just metres away from where my great-grandfather is buried and where my father worked among the flower-beds and the anguish of wrecked lives almost 60 years ago.