Engaged couple discover they are brother and sister when their parents meet just before wedding

Unnamed pair are expecting their first child and  had been together for five years

An engaged couple who dated for five years have been left in turmoil after their families met and they discovered they were brother and sister.

The woman, who is due to give birth next month, is devastated by the discovery that the father of her child is her brother. 

The couple, who met at university, had decided they wanted to introduce their single parent families to each other before they got  married.

Bombshell: The unnamed couple had been together for five years before they discovered, just before their wedding, that they are siblings

But at the meeting it emerged they were brother and sister who had been separated as small children.  

The unnamed South African couple are still in shock after making the discovery last Saturday.

The country's Sowetan newspaper reported that the siblings had been raised separately after their mother and father went through an acrimonious divorce.

It reported: 'Their parents separated when the woman was eight months old and the man was two years old.

'The man's father said he dumped his wife in 1983 because she was cheating on him. The girl was raised by her mother, while her brother was raised by his father.

'Neither of them knew they had a sibling.' 

THE POWER OF GENETIC SEXUAL ATTRACTION

Genetic Sexual Attraction (GSA) is a term that describes the phenomenon of sexual attraction between close relatives, such as siblings, first and second cousins or a parent and offspring who first meet as adults.

It is not the same as incest, though this is what it is called if a sexual relationship is then entered into.

The term GSA was coined 30 years ago by American Barbara Gonyo. She wrote a book about the lust she felt for the adult son she had given up for adoption 26 years earlier. 

She never acted on her feelings.

GSA is rare between people raised together in early childhood due to a reverse sexual imprinting known as the Westermarck effect, which desensitizes them from sexual attraction.

Experts believe that this effect evolved to prevent inbreeding.

The Sowetan reported that the children grew up separately with their single parents near the towns of Nelspruit and Bushbuckbridge, which lie 50 miles apart in South Africa's eastern Mpumalanga province.

They reportedly met again at university in 2007 and fell in love.

Their two families did not meet throughout their five-year relationship, until they were brought together last week to discuss wedding arrangements.

In many African cultures it is traditional for the family of a male partner to pay a lobola, or 'bride price', to that of his fiancée.

In doing so, the two families normally arrange a summit at which they are formally introduced and able to conduct the negotiations.

But the couple's plans were derailed when their parents came face to face and revealed their bombshell.

The woman told the Sowetan she was devastated by the revelation.

She said: 'It was love at first sight. We were studying together at Tshwane University of Technology in Nelspruit.

'When I first saw him, we connected. We fell in love and since that day, we never looked back.

'All we wanted to do was just to have a family and many kids.

'So you can imagine how shocked we were when they broke the news. We are going to have a child together. We do not know what we will tell him when he grows up.'

The couple said they had decided to split after hearing the news and were discussing how to handle the shock with their separated parents.

The man added: 'We can't think straight at the moment and will just take everything one step at a time.' 

Incest remains one of society's last taboos and is an unthinkable concept to most people.

Yet research by the British Medical Journal showed that half of those separated from relatives at a young age experience strong sexual feelings when they are reunited.

Psychiatrists believe the natural repulsion brothers and sisters feel growing up together as children acts as an inhibitor to incest.

But those who miss out on this time can develop powerful, obsessive feelings for their sibling in adulthood.