Two siblings are trying to fight for the right to make incest legal in Germany.

Biological siblings Patrick Syuebing and Susan Karolewski are wanting to make incestual relationships legal.

Syuebing had lost contact with his biological family after their now-deceased father attacked him with a knife and he was moved to foster care.

Over 20 years later, Syuebing went looking for his biological mother and was reunited with his younger sister Karolewski.

The siblings started sharing a bedroom after their mother died, six months after Syuebing had reunited with them, the Mirror reported. 

Back in 2001, the pair tried to change Germany's laws which makes sex between siblings illegal. This led them to take their case to the Court of Human Rights in 2012.

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At the time, Syuebing told the Daily Mail "we do not feel guilty about what has happened between us".

Now the couple is renewing their fight for change. The Mirror reported Syuebing has since had a vasectomy to try and prove to the courts they should be allowed to be together if they can't have children.

Syeubing does not believe he should be jailed for sleeping with his sister.

"I do not want to go back to jail and I know we will never voluntarily leave each other," he said. "If anyone doubts our love they should just see we will not be kept apart."

Karolewski, who is mentally disabled and seven years younger than her brother and lover, said in a statement: "We fell in love as adults and our love is real. There is nothing we could do about it. 

"We were both attracted to each other and then nature took over from us."

Incest laws were introduced in Germany when the country was under Nazi rule.