Adriana, 39, and her husband Leandro, 37, who did not want to share their surnames, have known each other for 10 years and now have a six year old daughter together.

Both Adriana and Leandro, who live in Sao Paulo, had been searching for their mother for a number of years. Leandro knew his mother was called Maria, and that she had abandoned him at the age of eight. He was brought up by his step-mother.

Adriana knew her mother was also called Maria, and that she had been abandoned at the age of one. She was brought up by her father.

The couple thought that their mothers, who they believed to be two different women, should the same name was a “coincidence,” as Maria is a common name in Brazil.

But Adriana’s refusal to give up the search for her mother led her to calling into to Brazilian radio station Globo Radio, and eventually managing to speak to her mother on The Time is Now programme, which specialises in finding lost relatives, the Mirror reports.

At the end of Adriana’s conversation with Maria, her mother revealed she also had a son called Leandro, who did not know her.

Adriana, shocked at the realisation that her husband was also her brother, said: “I don’t believe that you’re telling me this. Leandro is my husband.”

The phenomenon that Leandro and Adriana have experienced is called Genetic Sexual Attraction, and it occurs between “two adults who have been separated during the critical years of development and bonding and are reunited alter as adults,” according to a GSA website, which has now been turned into a GSA support-based forum.

In 2003, the Post-Adoption Centre, which offers information and counselling to people undertaking adoptee reunions, and which at the time was seeing 3,000 clients a year, estimated that up to half of reunions were accompanied by anything from temporary attraction to obsessive sexual obsession, according to the Guardian. A study by University College London found similar results.

The attraction that occurs between separated family members can been defined by people not having experienced what is known as the Westermark Effect, a hypothetical psychological effect that suggests people who live in close domestic proximity during the first few years of their lives together means they become desensitised to any later sexual attraction. People who experience GSA have supposedly not had this critical period of desensitisation together.

“Now I’m scared to go home and find out Leandro doesn’t want me anymore. I love him so much,” Adriana told her mother on the radio.

The couple were reportedly never married legally. Adriana said: “Only death is going to separate us. All this happened because God wanted it to happen.

“Of course it would have been different if we had known all this before, but we didn’t and we fell in love.”

Their case is not isolated, and the more extreme cases of GSA are prone to making national headlines; in 2008, the story of a pair of twins who were separated at birth but who later married was widely covered. They had been adopted by different families and completely unaware they were twins until after they were married. The marriage was annulled.

And GSA was even used as plot line in Neighbours in the early 2000s, when the character of Serena Bishop becomes immediately attracted to a new character, Luka Dokich, before discovering he is her half-brother.

In the case of Adriana and Leandro, they are determined to stay together, despite what “anyone might think”. Their attitude to their relationship reflects the findings of Dr Maurice Greenberg, who spoke to the Guardian in 2003, said it is essential to determine GSA as incest only in terms of biology, as the relationships that occur – even when sexual - are between two consenting adults.

Adriana said: "At first we were really knocked by it all, but we had a family meeting and told everyone that we are going to stay husband and wife, whatever anyone might think.

"We have so many plans together. Nothing is going to break us up. Nothing."