A couple who planned for a wedding after living together for five years, discovered they were brother and sister when their families met, The Daily Mail reported.

The woman in her ninth month of pregnancy is in a desperate state after learning that the father of her child is her brother, it reported.

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The couple in South Africa met at university and were going to introduce themselves to their parents before they got married.

But when their families met, the two found out that they were brother and sister who had been separated when they were kids.

"Their parents separated when the woman was eight months old and the man was two years old," Sowetan Newspaper, one of the country's English newspapers, said.

"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," it added.

However, the couple said they had decided to end the relationship after hearing the news.

The Daily Mail reported that the tragic couple may have fallen in love due to the power of genetic sexual attraction.

"Genetic sexual attraction is a term that explains the phenomenon of sexual attraction between close relatives, such as sibling, first and second cousins or a parent and offspring who first meet as adult," The Daily Mail reported.