'My dad had a secret family with the next-door neighbour. The way I found out was devastating.'

My father was a self-confessed ladies' man. He had photo albums of pretty women on fancy cars, all girlfriends in a previous lifetime, before he met my mum. He was a good-looking man (think Robert Redford) and moved from Melbourne when he was 21 to escape his past.

He told us he had been a boxer and into street fighting, and needed a fresh start, away from the bad crowd he was associating with. He married my mother and made his fortune building his own successful business from scratch, building a big house and having three beautiful blonde kids. Life looked to be pretty good.

His secretary at the business he owned, a pretty blonde lady called Laura, 12 years younger than him, soon became best friends with my mother. Everyone thought they were sisters, but truth is they both were only children and found a sister in each other. They became inseparable and when Laura married her partner Tim; they bought the block next door and built an equally big and beautiful house right alongside us.

We spent birthdays, holidays and many other occasions with Laura and Tim, who also went on to have three kids. Their eldest, a daughter Gemma, had been born just before my younger brother. They looked like twins and went to kindy together.  

The mums owned a business together and took it in turns to run things while the other watched the kids. 

Tim worked long hours and weekends, so Laura and the kids spent a lot of time at our house. My dad would walk them home safely next door at the end of every evening.

I noticed my dad's eyes would light up whenever he saw Laura and I could also see the feeling was mutual. As time went on, my friends and I caught them kissing at parties a few times. Sometimes they'd go on days out together and my mum would stay home and watch the kids.

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I was really mad at my father for thinking Laura was more beautiful than my mum. My father's affection for her was easy for me to see.

Time passed. Their family moved house but we still stayed close. We visited them on weekends.

Then, in the late '80s their marriage broke up. Laura met someone else and moved away with him.

My father seemed devastated.

My parents got divorced when I was 21, three years later. They had been angry and distant with each other for years. By this time I was starting my own life with my boyfriend, and had moved out away from the family. When I got married at 28, I invited Laura and her family to my wedding.

Sadly, Laura died suddenly from a heart attack later that same year. We were all shocked and devastated.

After this, her daughter Gemma and I became closer. We were both pregnant at the same time and ended up raising our daughters like sisters. 

We were quite like sisters too. We looked similar with our blonde hair and green eyes - people would ask us all the time if we were related. 

As an adult, I'd already begun to piece together that Dad had an affair with Laura - now I wondered if he might actually be Gemma's father, making us half-siblings. 

I broached it gently with my mum and sister, but they both told me I was crazy. 

I think they were both in denial. Gemma, however, shared my suspicions. She even had the same blood group as me and my dad - it was all too uncanny. 

My father died in 2011. Gemma came to say her final goodbye and told me she had asked him on his deathbed if he was her father. He had said no.

It wasn't until eight years later, that the truth came out. Dad's girlfriend Diane - who'd been with him until his death - called and said she had some information Dad had asked her to pass on some time after he was gone. 

She told me that Dad told her he and Laura had an affair for 15 years — (until she left Tim and moved away) and they had a child together, Gemma: who was raised next door, believing her father was Tim.

I already knew in my heart it was the truth. I had been gaslighted into not believing my intuition for so long.

I shared the information Diane had told me with my mum and my sister.

Mum was angry and heartbroken to hear of the betrayal. 

The news got to Gemma before I could speak to her myself. I text her repeatedly, and in the end, when she didn't answer me, I sent her a message telling her that our parents had had an affair and we were possibly half sisters, but she would need to get DNA test done to confirm.

She blocked me on social media and told my mum I was a liar. Her mother Laura was an "angel" and she wanted to remember her that way.

I was understandably upset, but respected her wishes to cut contact.

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Over the years I felt my mother and sister become increasingly distant and hostile towards me because "I knew" and they had "no idea". I felt at times like they blamed me. But I didn't have the affair and hide my child as "the girl next door".

Eventually they stopped speaking to me altogether and I haven't heard from either of them in years. 

Last year, Gemma messaged me out of the blue. She told me she had finally done a DNA test and we were in fact half-sisters. 

There was an offer from her of reconciliation.

I declined.

Because really, we are all affected by this deception and betrayal in some way. Our lives were a lie. I was devastated that I was ostracised from the family because of my father's actions.

But in the end, DNA doesn't lie.

Family are supposed to be people who love and respect you. Sisters are supposed stand by you through thick and thin.

Relationships are meant to be built on honesty and respect.

Except the ones in my family.

They are built on lies and betrayal.

Image: Getty.

The author of this story is known to Mamamia but has chosen to remain anonymous for privacy reasons. Names have been changed.