Five years ago, Karl and Inge gave their written permission for doctors at a local clinic to freeze Inge's eggs fertilized with Karl's sperm so they could have children later in life.
After divorcing each other, Inge forged Karl's signature twice to use a fertilized egg to become pregnant and gave birth to a boy.
The 37-year-old Karl had filed a lawsuit after he became legally obliged to provide child support following the birth of his son by his 42-year-old ex-wife.
A regional court in the southern German city of Munich ruled on Wednesday that he must provide financial support for his child who had been born without his explicit consent.
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In his lawsuit, Karl argued that he should not be legally obliged to pay child support because he had revoked his permission for the eggs to be used after he split from his wife. He also argued that the clinic should take over financial support for the child.
But the court ruled against him after finding that Karl was not clear enough when he called the clinic to revoke his consent for the fertilized eggs to be used. The clinic, it added, had no reason to doubt the authenticity of the forged signatures.
The decision, made by the court's medical malpractice section, is not legally binding.
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