A boy must leave the home he shares with his mother and grandmother in England and move to live with his father in Northern Ireland, a family court judge in London has decided.
The youngster, who is not yet 10, has been at the centre of a family court battle between his separated parents for six years.
Three years ago a judge had ruled that he should be in his mother's care.
But another judge has reviewed the case and decided the youngster should live with his father.
Judge Robin Tolson felt the boy's relationship with his father was being undermined by his mother and his mother's mother.
His grandmother felt that his father was "irresponsible".
She had called his father a "bad man" in front of him, the judge concluded.
Judge Tolson had analysed the case at a private family court hearing in London.
Detail has emerged after the boy's mother unsuccessfully challenged Judge Tolson's ruling at a public appeal hearing in the Family Division of the High Court in London.
Appeal judge Sir Andrew McFarlane said none of the woman's complaints about Judge Tolson's decision could be sustained.
Sir Andrew said, in a ruling on the case, that the boy could not be identified in media reports.