A businesswoman has been handed a bill for around £100,000 after a judge ruled that she had deceived her ex-husband into thinking he was the father of the son she gave birth to following fertility treatment.
Judge Deborah Taylor ordered the woman to pay £40,000 damages and pick up her ex-husband's lawyers' bills - said to total about £60,000 - after a trial at Central London County Court.
She was told that the man - a lecturer - had earlier offered to settle the litigation if his ex-wife paid him £12,500.
The man had complained that, without his knowledge, the child was created using sperm provided by a former boyfriend - and claimed damages.
He said she dropped the ''bombshell'' when the child, now nine, was five years old.
The woman said there was ''no merit'' in the damages claim.
She said she always thought her ex-husband knew he was ''not necessarily'' the boy's father.
Judge Taylor analysed the case at a hearing earlier this week and ruled in favour of the man today.
She concluded that the man's claim for "deceit" was "made out" and said there had been "deliberate fraudulent misrepresentation" by the woman.
The judge was told by a lawyer involved that the case was thought to be the first of its kind.
She said nothing could be published which would reveal the identity of the boy at the centre of proceedings.
Judge Taylor said the man and woman should be referred to as ''X'' and ''Y''.
The judge was told that the man is in his 60s and the woman is in her 50s.
They live in different parts of the London area. The man also has family links to Bolton in Lancashire, the judge heard.
Judge Taylor heard that the couple married in 2002.
In 2004 they travelled to a clinic in Barcelona, Spain, for IVF treatment and the man gave a sample of his sperm.
A few months later the woman returned to the clinic without him, travelling instead with a former boyfriend.
Barrister Thomas Brudenell, who represented the ex-husband, said that, during the later visit, the woman was impregnated with her former boyfriend's sperm.
The little boy was born in late 2005 and the couple separated when he was around six months old.
Divorce proceedings began and their divorce was finalised in 2008.
Mr Brudenell said the man looked after the child when the woman was working and paid more than £80,000 in maintenance over the following few years.
In 2011 a dispute arose over the amount of contact he was having with the youngster - and the woman then told him that he was not the ''biological father''.
Shortly afterwards that was confirmed by a DNA test.
The woman told the judge that she had never told the man he was the father and said she had hidden nothing.
She said her ex-husband knew ''from the very first day'' that she had been to the clinic with her former boyfriend.
The woman said there had been no deceit, no fraud and no misrepresentation - and she was ''not guilty''.
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.
He said the man's work had suffered and his income dropped because he was ''shattered''.
Judge Taylor heard that the couple's marriage was in difficulty around the time the woman had IVF treatment.
She was told that they had drawn up an agreement under which the man would not have the ''normal'' financial responsibility for any child.
She said that ''upset'' the woman.
"I found the woman to be an untruthful witness," said Judge Taylor in her ruling. "I found her account both highly improbable and inconsistent."
The judge added: "She presented herself as a victim of circumstances rather than a participant."
Judge Taylor went on: "I found (the man's) evidence more consistent." The woman had "represented" that the man was the father of the child.
Judge Taylor said that was "untrue to her knowledge throughout". The woman knew that the boy was her ex-boyfriend's child.
"I am satisfied that(the woman) intended (her ex-husband) to believe that he was (the boy's) father," said Judge Taylor. "I reject her suggestion that she believed (the boy) may not be (her ex-husband's) child."
She said there had been "deliberate fraudulent misrepresentation" by the woman and the man's claim for deceit was "made out".
Judge Taylor said the man should get £10,000 damages for the distress he had suffered, £4,000 for loss of earnings and more than £25,000 as compensation for the maintenance he had paid.
She said the woman, who represented herself at the trial, should also pay the man's legal costs - which sources said were around £60,000.
Mr Brudenell told the judge that the man had offered to settle before the trial for a payment of £12,500.
Judge Taylor had been told that the man had now lost almost all contact with the little boy.
The man said after hearing that litigation had been "incredibly difficult".
"I have sometimes felt, 'I think I am in the wrong film'," he told reporters. "I can't imagine what my then 'son' must have felt to have had a loving father substituted by another man."
He added: "I live in the hope that when he is 18 he looks for me ... He is truly missed."
His solicitor, Ellen Windsor, added: "I am pleased that the law was able to find a remedy. This was very modern litigation, made possible by developments in DNA technology. And no-one should underestimate how this man has suffered - and it will continue."
The woman left court without speaking to journalists.
A lawyer who specialises in family cases said later that the judge had sent a "clear message".
"The family courts have always been clear that they expect children to be told the truth about their biological origin, whether in cases of adoption, surrogacy or gamete donation and that it is the right of the child to know where they come from, not least to avoid confusion and shock in later life," said Cara Nuttall, who works for law firm Slater and Gordon.
"This decision makes it clear that the court not only considers that it is usually in the child's best interests to know the truth, but that there is no place for deception in respect of such fundamental matters within a family."
She added: "The judgment sends 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."