Disowned by her family and banished to a convent for getting pregnant as an unwed teenager, Philomena Lee was forced by the nuns to give her son up for adoption to an American couple.

The new movie 'Philomena,' starring Judi Dench in the title role, about the woman's journey to find her son, will premiere this week at the American Express Gala at the BFI festival in the UK.

"For years, I couldn’t talk about my life to anybody. And now it is all anyone wants to talk about," Lee, now 80, told the Daily Mail in an interview.

In her home is a portrait of a man dressed in a pinstriped suit and tie and wearing a warm smile. Her son became a prominent attorney and highly respected figure in Republican Party politics. However, we was privately a gay man and in the 1980s died of AIDS.

He had tried to find his mother and went to Ireland  but was rejected by the nuns who would not give him the information. In the end in his will he asked to be buried in the garden of the convent as he knew his mother would find him there some day -- and she did.

‘Every day I think, “If only I could put my arms around him one more time,”’ says Lee of the son she had a few weeks after she turned 19. ‘He looks to me like the type of chap who would have wanted that.’

Lee never got the chance to get to know the son, born in 1952, who she named Anthony.

The nuns who took Lee in only allowed her to see her son for an hour a day, until, when he was three and a half, the child was placed in the back of a car and driven out of her life.

"In my dreams that moment still comes back to me," she says. "I see his little face looking through the rear windscreen – I’ve relived it so many times."

"I cried out his name, and I didn’t stop crying for two weeks,"  she recalled.

No one would tell Lee where her son had been taken, only that the church had found a good Catholic family that could provide a home for him. She was forced to sign a pledge of surrender, and the Mother Superior told her she would 'burn in the fires of hell' if she ever told anyone about her 'shameful secret.'

Lee kept that secret for nearly half a century until she and her daughter Jane went on a journey to find her first-born son.

The film, which debuted at the Venice Film Festival, is based on the 2009 book "The Lost Child of Philomena Lee" by Martin Sixsmith. Lee traveled with Sixsmith, played in the movie by screenplay co-writer Steve Coogan, on a journey to America to find out more about her son, who died in 1995 at the age of 43 before Lee ever had a chance to see him again.

Lee has seen the film twice, and says "the first time was stressful, but the second time I enjoyed it, and I was so glad that they didn’t harp on about the Catholic church because I wouldn’t have wanted that."

Lee says she got on well with her on-screen counterpart.

‘She got me to a T – I felt I had known her all my life,’ says Lee.

At a press launch, Dame Judi said Lee had a ‘lively sense of humour’ and that she was awed by Lee's capacity for clemency: ‘I wish I could say that I would have her scope to forgive but I doubt if I would. It’s what makes her story worth telling.’

Says Lee, ‘I would have given anything to have Anthony here beside me, but the worst thing all those years was the not knowing. At least now I know that he is at peace and because of that, I, too, can have peace in my heart.’

The film 'Philomena' will be released on November 1. Here is the official trailer: