Last week, Karen McKenna's father, George McKenna, was listening to Liveline. Suddenly, he came into the room his daughter was in and excitedly asked her if she had been listening to the radio.

"There's after being a woman on Liveline: Liz McKenna," George told his daughter.

"He had the biggest smile on his face and he said, 'I wonder if she could be my sister.” relayed Karen.

Liz McKenna had been speaking to Joe Duffy last Friday about the circumstances of her birth: all she knew is that she was born in 1940 in the Rotunda Hospital in Dublin to a Mary McKenna – later thought to actually be a Mary Lang – and was baptised at Dublin's Pro Cathedral. She also knew that, as well as giving birth at the Rotunda, her birth mother had also worked at the hospital.

Beyond that, Liz really didn't know much about where she came from. As a child and young adult, she was passed from Billy to Jack, living in orphanages and being sent to various foster homes around the country. She knows she was sent to the Convent of Mercy in Newtownforbes. She remembers a dormitory with a large crowd of people. She doesn't remember school, but she remembers being chastised by nuns. At 19, she went to London. She told Joe, "I just want to know who I am."

Parallel to this, George McKenna, Karen's father, who had been born a year later in the Rotunda, in 1941, was living with his great aunt in Cabra. George had also been born to a Mary McKenna who worked at the hospital, and was also baptised in the Pro Cathedral. He was subsequently given to his birth mother's aunt, Elizabeth Nolan (nee. Bermingham), who raised George as her own.

Coincidence?

"There has always been talk of a possible older sister," said Karen to Philip Boucher-Hayes, who presented Liveline today.

"We've had people looking into it over the years. My dad remembers his mother, she came to see him. The last time he saw her, she took him out to Blackrock – and my dad had an awful habit of messing with the handles on doors as a child – and she told him that if he didn't stop messing with the handle she'd send him back to Cabra. Being a three or four year old, my dad did it again and he was marched back to Cabra," she said.

"We would have asked [family] over the years, and my dad was always told, 'you don't need to know, that's fine'. As far as they were concerned, he was their brother, their son; that was it."

"We were never given the full story. I think it was looked at that we were family, they reared him, and that was that," said Karen.

"The kernel of this is," said Philip Boucher-Hayes, "a Mary McKenna who worked in the Rotunda, giving birth in the Rotunda, a year apart to a boy and to a girl, and her possibly being called Lang. That's the heart of this."

Liz McKenna thought nobody had ever come looking for her. Now, it's possible that she might well have a brother who has been looking for her all along.

"Liz was saying that she puts her heart and soul into everything; I'm exactly the same!" said George to his daughter.

"We could be making all sorts of assumptions about this, said Philip, "but what are the chances?

"We'll take this information, we'll run with it and see where it leads us. At face value, it's very, very promising, isn't it?"

We'll keep you updated. You can listen back to the full story here.