Patrick S. was sentenced to 2 ½ years in 2005, Deutsche Welle reported. He has already received a suspended sentence and served 10 months for previous convictions.

Susan K. has never been given a custodial sentence because she was treated as a young offender.

While they are biologically siblings, the couple were brought up separately. Patrick, adopted by a family in Potsdam, discovered his mother and sister in 2000 when he decided to seek his biological family.

Endrik Wilhelm, a lawyer representing the couple, said they will ask the Constitutional Court to throw out Germany's anti-incest law. A number of countries, including France, Belgium, the Netherlands and Portugal, have already removed such laws from the books.