As my beloved mum lay on her deathbed, she turned towards me and said, "Louise, I have ­something I need to tell you." The look on her face told me it was serious. "Your dad wasn't your biological father. He adopted you when you were three years old."

I couldn't believe what I was hearing. Overwhelmed, I wanted to run away. But Mum held my hand, determined to keep speaking while she still could. "One night when I was 21, I was on my way home from work in Glasgow when I was raped by a stranger, which resulted in me becoming pregnant with you.

“I'm sorry that I haven't told you before, I didn't know how. I've always felt guilty about keeping it from you and I hope you can forgive me." The revelation floored me. I pulled away and fled the room. Struggling to breathe, I felt as though my whole world was crumbling. But there was no time to fall apart.

After composing myself, I went back to my mum's bedside as she took her final breaths with my sisters, Amber and Lucy, next to her. Stroking her head I said, "It's okay, Mum." And with that, she passed away. I was numb with shock and grief. I looked over at Amber and she nodded at me. In that moment I ­realised she knew the awful truth too. It turned out our mum had confided in her a few years earlier, and although she wanted to tell me, mum begged her to remain quiet.

Louise was shocked to find out who her real father was

I started to cry so hard that I didn't think I'd ever stop. The next few days were dreadful. My sisters organised my mum's funeral because I couldn't cope. In the months that followed, I ­realised I'd always wondered about my dad, who had died 10 years earlier from motor neurone disease. I look completely different to my sisters and growing up, Dad was always slightly indifferent towards me. I had a privileged upbringing in many ways, with everything I could want in material terms, yet I always felt separate from the rest of my family.

While my mum and sisters would play silly games and laugh together, I didn't get their humour. My home life could be turbulent. My dad was ­physically abusive to my mum, and although he never hit me or my sisters, we witnessed him pushing and hitting our mum. After several particularly bad rows we had to flee the house and stay with friends. But Mum always went back to him. It was sometimes a source of resentment between the two of us and I wish that she'd been strong enough to leave him.

We lived in fear of Dad's temper and even minor annoyances like a traffic jam would send him into a violent rage. My sisters had the ability to placate our dad in a way I couldn't. But my mum and I had a great relationship. Whereas Amber and Lucy were very close in age and spent a lot of time together, if I wasn't reading in my room I would seek her out.

Aged 17 I left our home in Surrey and went to live in London, where I combined studying at college with work. Although Mum begged me not to leave, Dad agreed I was old enough to make my own way. Once I left home, I saw him even less. Whereas my mum frequently came to visit, dad rarely did.

When my dad died, I didn't really know what to think. Part of me was sad, but I was also relieved. After Mum lost my dad, she grew closer to my sisters, particularly Amber, and the pair of them frequently visited. There were times I was a little envious of their bond. Living in London wasn't always easy and throughout my 20s and 30s, there were times when I was quite depressed.

I had a job in social care which could be very stressful, and while I loved helping people, it meant I was dealing with people who were homeless or addicted to drugs. I did my best to stay well with ­antidepressants, regular exercise, eating well and surrounding myself with positive people. But learning the truth about my biological father hit me hard. Not long after my mum died in 2004, I spiralled into a very dark place.

I applied for a credit card and went on a crazy spending spree, racking up ­thousands of pounds of debt in a few months. Buying things was the only thing that temporarily took away the pain inside of me. I saw psychologists and psychotherapists and was diagnosed with bipolar disorder, depression, anxiety and psychosis.

Knowing that the mother I adored was attacked caused me so much suffering and guilt. For years I felt like I didn't deserve to exist. It's taken a lot of work in therapy to know that's not the case. Now I'm older I have found a kind of peace. I realise that my dad tried to be a good father to me in his own way. He adopted me, supported me financially and even tried to get me a job.

I'm also lucky that I'm close to my younger siblings who have been there for me through some very bleak times. And I have nothing but love and compassion for my mum. I know she must have loved me very much in order to go through with the ­pregnancy and then to keep me after I was born.

Life was very different for single mothers in the 1970s and her family weren't supportive. Yet her love for me meant that she faced what must have been a very difficult situation. Despite a challenging life she was the most loving, caring woman I've ever encountered. She had the ability to laugh no matter what and always believed that something amazing was going to happen.

The years before her death were her happiest and she had found the ­contentment that she'd always craved. She adored her daughters, and subsequent grandchildren, and I believe that everything she did was with the right intentions. My only wish is that she had told me her secret sooner.

My sisters and I have all worked hard on being close and they are very protective of me. I'm glad my mum felt like she could confide in Amber, while she plucked up the courage to tell me. I’m glad to know the truth.

As told to Natasha Harding

  • Names have been changed