On Easter Sunday in 1908, the Catholic Church's Ne Temere ruling came into force.
It meant the Catholic Church would not recognise a marriage between a Protestant and a Catholic unless it took place in a Catholic church. It also decreed children from the marriage must be brought up as Catholics.
In the BBC Radio Ulster documentary, Mixing Marriages, reporter Barbara Collins looks at the effect the Ne Temere ruling had on one family 100 years ago. She tells BBC News Online why she wanted to make the programme.
I had never heard of the Ne Temere decree before I started working on this documentary, and I certainly had no idea of its impact on the Home Rule movement.
But what attracted me to this programme was the harrowing story of a young mother, 100 years ago, desperately searching the streets of Belfast for her two babies.
Her children had been taken by her Catholic husband because she, as a Presbyterian, refused to comply with the Vatican decree to remarry in a Catholic church and bring the children up in that faith.
As a mother of a 20-month-old boy, I could imagine how utterly devastating it must have been for her to lose those dearest to her at such a tender age, and for it to happen at the hands of the man she had once loved.
Agnes McCann's name became known the length and breadth of Ireland and beyond.
Her story became a propaganda tool for the anti-Home Rule movement - rallying Protestants who feared that there would be more young mothers like Agnes forced to either deny their faith or lose their children and their homes.
Historians claim that the McCann case, was one of the key reasons for the defeat of the Third Home Rule Bill at Parliament, some even go so far as to link it to the partition of Ireland.
Agnes, seemed to be the victim in all of this.
Was her husband, Alexander a cruel, heartless man to insist that she consent to the demands of Ne Temere?
Copies of love letters I found showed they had loved each other and I began to wonder if the whole family were pawns in a political game.
The priest who visited their home in west Belfast in 1910 convinced Agnes's husband Alexander he had been living in sin and his children would be damned. Alexander felt he had no choice but to take them from her if she wouldn't capitulate.
Historical records paint a picture of a woman who never recovered from this tragic incident in her young life.
Despite frantic searching, nationwide publicity and beyond, Agnes McCann never saw her children again. She was reported as being "broken in health, suffering untold agony of the heart".
I wondered what had happened to Alexander and the two babies, but despite weeks of research, I drew a blank.
He was never heard of again. Some references to the children suggested they were "beyond the reach of Ulster's guns"; that they were in a convent in Longford, but nobody really knows for sure.
The likelihood is that Alexander remarried and brought the children up as Catholic, or they may have been placed into an institution.
Agnes, who bore the trauma of separation, died without ever knowing her children's fate and, subsequently, they would have no memory of their mother.
It would seem Ne Temere had a lot to answer for.
Mixing Marriages can be heard on Thursday, 11 November at 7.30pm. 92-95FM & DAB digital radio, digital TV and online at bbc.co.uk/radioulster now.