A Dutch court has banned a man from donating any more of his sperm after he fathered at least 550 children in the Netherlands and beyond.
The man, named Jonathan, 41, also misled prospective parents about the number of offspring he helped to conceive.
He was ordered to immediately halt all donations and must pay 100,000 euros (£88,000) per case if he breaches the ban.
Under Dutch guidelines, sperm donors are allowed to produce a maximum of 25 children with 12 mothers.
The court also noted that the donor lied to prospective parents about his donation history.
A judge, at The Hague District Court, ordered the halt in an injunction, which was brought by the mother of a child conceived with the donor’s sperm and a foundation representing other parents.
The mother, identified by the foundation only as Eva, welcomed the court's decision.
"I hope that this ruling leads to a ban on mass donation and spreads like an oil slick to other countries," she said in a statement.
"We must stand hand in hand around our children and protect them against this injustice."
The donor provided sperm to several Dutch fertility clinics, a health centre in Denmark and a number of other people he connected with through advertisements and online forums, the court said in its written judgment.
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The donor's lawyer said in a court hearing that he wanted to help parents who would otherwise be unable to conceive.
Meanwhile, the judge who heard the civil case said that the donor "deliberately lied about this in order to persuade the parents to take him as a donor".
"All these parents are now confronted with the fact that the children in their family are part of a huge kinship network, with hundreds of half-siblings, which they did not choose," the court said.
The court added that the case was about "conflicting fundamental rights".
"On the one hand, the right to respect for the privacy of the parents and the donor children... and on the other hand, the same right of the donor," the court said.
Lawyer Mark de Hek called the ruling "a clear signal and, as far as I am concerned, a final warning to other mass donors".