A woman who conned her former husband into believing he was the father of her IVF baby has been ordered to pay £39,000 in damages at the High Court.
The London businesswoman carried out "six years of deception" on her ex-partner, a judge was told. Neither can be identified for legal reasons,
The man said the boy, now nine, was five when she told him the truth.
He had claimed the child was created without his knowledge with the use of sperm from a former boyfriend.
He was said to have suffered considerable "distress and humiliation" when he found out.
Judge Deborah Taylor made the ruling following a hearing of the evidence at Central London County Court at which the couple were referred to as X and Y.
She ordered the woman to pay the damages, plus interest.
The couple married in 2002 and two years later they travelled to a clinic in Spain for IVF treatment, where the man gave a sample of his sperm.
A few months later the woman returned to the clinic with a former boyfriend.
Barrister Thomas Brudenell, who represented the man, said during the later visit the woman was impregnated with her former boyfriend's sperm.
The boy was born in late 2005 and when he was around six months old the couple separated.
The man looked after the child when the woman was working and paid more than £80,000 in maintenance, his lawyer told the court.
When a dispute arose over the amount of contact he was having with the child in 2011, the woman revealed he was not the "biological father" and this was confirmed when he took a DNA test.
'Distress and humiliation'
Mr Brudenell said the couple had drawn up an agreement prior to the IVF treatment under which the man said he would not have the "normal" financial responsibility for any child and it seemed the agreement had "upset" the woman.
The woman had asked whether any "normal, loving, caring, husband" would have "forced his wife" to sign such an agreement.
"He didn't want to go back [to the Spanish clinic]," she said. "The only reason I took [my ex-boyfriend] was because my ex-husband gave me that document to sign.
She told the court there was "no merit" in the damages claim, saying she had always believed her former husband was aware he was "not necessarily" the boy's father.
She said there had been no deceit, no fraud and no misrepresentation.
Mr Brudenell told the court that the man wanted damages for "distress and humiliation", damages to cover the amount he had paid in maintenance, and compensation for loss of earnings.
Speaking anonymously to BBC Radio 4's PM programme the man revealed he had been refused the right to continue seeing the child after a separate court case.
"Now I have to wait until he is 18 and by then who knows," he said.
"I don't regret any of the time I spent with my child at all. I don't regret that ever, but when someone actually comes along years later and spoils everything that way, you're revisiting all those experiences thinking, that wasn't right was it, and not for him either."
Cara Nuttall, a lawyer who specialises in family cases said the judge had sent a "clear message to parents that concealing the truth from each other is unacceptable".
"What parents must remember however is that whilst financial damages are one thing, the emotional and psychological impact such deceit can have can have far more devastating consequences."