An incredible coincidence has led to an Irish-born mother in Boston re-uniting with her only son after forty years.

When Bridie McMahan was 20 back in 1970 she had an experience that marked her for life.

McMahan had just arrived in America from County Galway as a recent Irish immigrant, and she quickly got a job working in a Dorchester rectory, where she was treated well.

But McMahan had a private worry--she was pregnant. That worry saw her check into Boston City Hospital weeks later where she eventually gave birth to a healthy baby boy, born out of wedlock.

The following morning, she had her first and last look at him through the plate glass of the maternity ward.

That was 40 years ago, and the following four decades were filled with unanswered questions for Bridie about her son. Adding to her pain was the fact that she had no subsequent children.

She says she accepted that as punishment for her youthful sins

What McMahan didn't know was that her son had a new name - Brian Wilkins. He was raised only miles from her own home by doting Irish-born parents who gave him a private school education - and he had grown up to be a fine parent himself.

McMahan never knew that she and her son had lived all their lives just a few miles apart, or that indeed, she used to jog by his house. She also didn't know he had a burning desire to find his birth mother too.

Then one day in August 2009, McMahan’s sister Helen took a call from her dental hygienist at her Quincy, Massachusetts apartment.

She asked her if Helen was one of 14 siblings, if she was from Galway and if she had a sister named Bridie? The answer was yes to all three questions

Then the hygienist told her that a woman named Dawn Wilkins, who worked with her, had married a man named Brian who was looking for his birth mother. Dawn had mentioned the last name and the sibling named Helen. Could she be the sister of Brian’s mother?

For Bridie McMahan it was a dream come true. Mother and son met in Brian’s Weymouth home in which his mother said, 'I finally get to hug you,' and Brian told her he’s had a great life, with no regrets, and that, 'You’re part of the family now.'

Meanwhile Bridie and Brian’s adoptive mother Maura Wilkins met for lunch at a local cafe. They bonded immediately and in Brian’s words have been 'Like two sisters ever since.'

Now they join forces to mind the grandsons, Declan, 2, and Desmond, 3, and they make family trips with the boys to places like Canobie Lake Park.

'It’s the best gift I could ever get,' McMahan told the press. 'I never thought it would happen. It’s really completed everything.'