'Sometimes I feel as if I didn't come from her,' I confessed to my friend. 'I feel so detached...'
Taking a sip of wine, I sighed.
A friend and I were chatting about our mothers, and while what I was saying about mine might sound a little heartless to many people, it was the truth.
The relationship between me and my mum Kathleen had always been strained.
Growing up, I felt like an outsider.
But neither my older sister, Margaret, nor my younger sister, Bernie, who Mum and our dad, Jimmy, fostered when I was two, had the same issues with her.
When Dad died when I was 16, I left our home in Dublin to move to the south coast of England to work as a teacher.
Decades went by with very little contact between Mum and me, and by the time I was 48, we hadn't really spoken for years.
But when my friend suggested I actually talk to my mum about our relationship, I realised I did need to get to the bottom of why we didn't seem to connect.
Ringing my uncle Pat, Mum's brother, I told him I was flying home to discuss things.
To my astonishment, he started crying.
'She has to tell you the truth,' he blurted out.
What did that mean? Probing him about it, I wasn't prepared for what he was about to tell me.
'You're not Kathleen's child,' he said. 'You're adopted.'
I was absolutely dumbfounded. How could this be? I was 48 years old.
My parents' names were on my birth certificate... How could I have not known?
Phoning Bernie, now 58, in Dublin, I told her the shocking news.
'Oh god, who told you?' she gasped.
It seemed she and Margaret had known since they were teenagers but had been sworn to secrecy.
I was the only one who'd been kept in the dark.
In a flash, all those years of feeling different suddenly made sense.
I was different. My whole life had been a lie.
Flying to Ireland the next day, I confronted Mum. 'Yes it's true,' she admitted sadly.
Mum explained that in 1954 she'd been approached by a local woman whose daughter was a social worker.
The woman said she knew of a girl who was giving birth soon, but couldn't keep the child.
'She asked if I was interested in taking on the baby,' Mum said. 'I was desperate for another child so I agreed.'
I was apparently born on June 9, 1954 in Dublin and Mum said that two days later I was ready to collect.
Mum went to the home of a local midwife to get me and it turned out she had been given 45 pounds - the equivalent of $80 - by the doctor to pay for the expense of keeping me.
It was as if I'd been sold.
Adopting a baby that way was illegal, but six weeks later Mum and Dad registered me as their own child.
My head was reeling as I asked Mum what she knew of my birth mother.
All she could tell me was that she thought her name might be Bridget.
That day, I left Mum's place with my head in a spin.
I didn't blame Mum for taking me in, but I did resent her for not telling me the truth until now.
At the same time, another feeling overwhelmed me. I had to find my real mum.
But I had no idea where to start.
Returning to the UK, I got in touch with the Irish authorities, asking them for any information.
It took a long time to get answers but finally I was sent a file. In it was a form setting out the adoption and showing that money had exchanged hands as I was handed over in 'good' condition.
There was also an index card stating that I was originally called Margaret O'Grady.
After that though, the trail ran cold and it's now been 12 years since I uncovered the shocking secret about my past.
I'm a mum myself to Tara, now 37, and Ryan, 33, and it pains me that I'm still no closer to finding my own birth mum.
Over the years I've wondered if my birth mum emigrated to Australia. Falling pregnant with me would have caused a scandal in those days and she may have moved to escape it.
I realise that, even if she's still alive, she will be a great age and I do not wish to upset her, but I've written her an open letter about how I feel.
As for Mum, I don't blame her for taking me in, but I struggle to accept why she didn't tell me the truth earlier.
It shatters me to think I was handed over like a parcel all those years ago.
I am now 60 and although my search for answers goes on, I fear I will never know who I really am.
Letter to my mum:
I know it must have been difficult for you to hand over your baby, but what choices did you have in the 50s - none? I just want to know what happened to you and that you went on to have a happy life. I hope from the bottom of my heart that you did.
Theresa's adoptive mum, Kathleen Hiney, now 90, says...
What I did was illegal and it is something I will live with till the day I die. It is something I can't undo and my heart aches for Theresa's hurt.
When I took her to be baptised, I could not bring her to the church without a parents' name on the certificate.
I'd had one child who was five by then and, desperate for another, my maternal instinct overrode any anxiety I had about what I did.
I told Theresa all I know. I pray she finds her birth family. I still call Theresa my daughter.
I love her but I did a terrible wrong and it is not easy to live with that.
Originally published in that's life! Issue 2, January 2, 2015