A devoted father who discovered that two of his three children had been fathered by another man is suing his ex-wife for compensation.

The millionaire businessman is demanding unlimited damages of more than £300,000 from his ex-wife and her new husband, including the cost of bringing up the two children he believed were his for more than a decade.

The man, who was the woman’s first husband, raised the two children as his own — with no clue that they had been fathered by his wife’s lover.

He accuses the pair of fraudulent misrepresentation and deceit, and says he has not been allowed to see the two children since 2006.

The details of the tangled relationships between him, his former wife and her second husband are exposed in court papers.

The businessman and his wife met in 1985 and were married a year later. They had business dealings with the man who would become the woman’s second husband from 1987, a High Court writ says.

The man, also married at the time, visited the couple at their home several times.

The tycoon’s first child was born in 1989 and, within months, the new mother had started a sexual relationship with her lover, the writ claims.

She then claimed that her second child, born in 1993 and had serious health problems, was fathered by her husband when the real father was her lover, it is alleged.

The wife and her lover resolved between them to claim the two younger babies were the millionaire’s natural children, and were involved in a joint enterprise to induce him to accept paternal and financial responsibility, the writ claims.

They did nothing to dispel his erroneous belief about the two children’s paternity, the writ alleges.

The writ details a series of personal questions apparently asked by the woman’s lover at a New Year’s Eve party in 1994, including: “How does it feel to have a son that was close to death?

“Are you and your wife going to have more children? Where does your second son get his lovely curly hair from? Yours and your wife’s is so straight.”

In August 1995, the tycoon’s wife carried out a pregnancy test and told him he was going to be a father again. Her daughter was born in 1996 and her husband was registered as her father.

In 1997, three employees commented on the uncanny resemblance of the tycoon’s daughter to a child born to his business associate — the man alleged to be having an affair with his wife.

The man is said to have told one employee that the child was his daughter. The employee passed the information to another colleague, but neither spoke of the matter for fear of losing their jobs.

The millionaire says that he supported his ex-wife’s second and third children as his own until 2007.

In 1997, she told him of the affair during a family holiday — but insisted that it had began after the birth of her daughter, the writ says.

She later admitted the affair had lasted several years, but reassured her husband that the three children were his.

The tycoon says he confronted his rival after returning from his holiday and, within months, entered into a deed of separation from his wife, sharing the children on a rolling four days each basis for eight years, making significant financial provision for her.

In 2003, he married the children’s nanny and fathered two more sons with her. His former wife’s lover divorced his partner in 2001 and the pair were married a year later.

The two families continued to share the children until the millionaire’s ex-wife arranged for DNA testing on her two younger children without her former husband’s knowledge, the writ says.

The woman and her new husband took the two children abroad on holiday in July 2006 and have refused to allow the millionaire to speak to them or see them since.

He discovered that he was not their natural father in a letter from his ex-wife’s solicitors, which caused him severe distress.

Later, court-ordered DNA testing showed that his former business associate was 5.5 million times more likely to be the boy’s father and 21 million times more likely to be the girl’s parent.

The spurned tycoon says he has suffered the cost of financially supporting the two children between their birth and July 2007 which should have been borne by his ex-wife and her new husband and he is seeking damages for deceit.

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