Aman discovered the three children he had had with his ex-wife were not his when his doctor told him he had been infertile since birth.
Richard Mason sued Kate, his wife of 20 years, when a doctor told him in 2016 that he suffered from cystic fibrosis and was incapable of having children. That meant the children he had raised as his own since 1995 must have been conceived during an affair.
The 55-year-old businessman, who co-founded Moneysupermarket.com, tried to get a £4 million cash sum paid as part of his divorce settlement in 2008 returned, while also pursuing his ex-wife for paternity fraud.
Mrs Mason agreed at the end of November to settle matters with a payment of £250,000 – on condition the biological father remained anonymous.
Roger Terrell, a solicitor representing Mr Mason, told The Telegraph the move may have been prompted by a desire to stop the identity being disclosed in court.
He said: “I think it was the major reason for her settling. I was shocked and surprised that she settled, I thought we were going to have a very acrimonious court battle.
“We were confident that we would get a court order whereby the ex-wife, the mother of the children, would have to name the father.
“She didn’t want to name the father – why, we don’t know – that is why she came to a financial settlement and in the settlement she did not have to name the father.”
Mr Mason hopes that speaking publicly will bring further details of his wife’s affair to light and appealed for the man to come forward for the sake of the children.
However, a source close to the family said the sons “don’t want to know” about their biological father as they are “trying to get on with their lives” and still consider Mr Mason their true parent despite two of them no longer talking to him.
The source said his decision to go public had come as a “shock and surprise”, adding: “I assume the natural father, whoever he is, has not made any contact and no doubt doesn’t even know they exist.”
Mrs Mason admitted that in the late 1990s she had been having an irregular, four-year affair with another man. Her eldest son was born in the 1995, while his brothers – twins – were born in 1999.
Few further details were disclosed, except that the man was a colleague at Barclays bank whom she met whenever she visited London in her role as a union official.
Mrs Mason’s had insisted that each son should have a Jewish middle name and her former husband, who now lives with his new wife in Rhos, North Wales, believes this detail could provide a clue to the biological father’s identity.
“I think there will be somebody who worked with him and her in Barclays who will know who it is and will tell us,” his lawyer said.
Mr Terrell believes the case is a legal first, as there are no other known instances where a financial settlement has been set aside due to alleged paternity fraud.
He told the Mail on Sunday the discovery was like “suffering a bereavement”, adding: “In an instant I discovered I didn’t really have any children…if I could wave a magic wand, I would want to be in all their lives.”
Mrs Mason, who lives Uttoxeter, Staffordshire, was unable to be reached for comment.