A High Court judge has given social workers permission to keep the existence of a toddler a secret from his half-brother and half-sister.
Mr Justice Cobb heard that the 15-month-old boy was living with a couple who want to adopt him - and concluded that revealing his existence might disrupt his new life.
He granted an application by lawyers representing a council with welfare responsibility for the little boy.
The judge analysed evidence at a private family court hearing in Leeds in January and published a ruling on Thursday.
He said no-one involved could be identified.
Mr Justice Cobb said the three children had the same mother but different fathers.
The judge said the toddler's half-brother and half-sister were both older.
He said the toddler had never met either.
A social worker told the judge that the toddler was thriving with his new family and she said "no step" should be taken to disrupt that placement.
"I do not think that (the toddler) would suffer harm," she said.
"It is not uncommon within adoption situations for children to grow up without a full awareness of their birth family."
The boy's mother said she wanted him to have a life "uncomplicated by any relationships with his birth family".
She said she was "fearful of harassment" if one of her other children's fathers knew about the toddler.
The couple who want to adopt were also opposed to information sharing, saying there was the "potential for serious emotional consequences to many people".
"Having reviewed the various welfare factors, I am persuaded to give effect to the wishes of the mother, and the view of the (couple who want to adopt)," said Mr Justice Cobb.
"I attach considerable significance to the value of the current placement, and the ... fear of disruption if contact of any kind were ordered."
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