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His debts of about £700,000 are to be paid off by the heiress, who had always agreed to that.

Ms Radmacher’s lawyers argued that Mr Granatino, who is French, was heir to a family fortune of up to £20 million and that he had originally planned to become an investment fund manager specialising in biotechnology companies on completion of his PhD, although he now intended to remain an academic.

Mrs Justice Baron, in the High Court, had ruled that it would be “manifestly unfair” to hold Mr Granatino to the deal, given the respective financial strengths of the two sides.

The judge also had some concerns that the prenuptial agreement was defective in that Mr Granatino had not had independent legal advice and there had not been full disclosure of assets.

Ms Radmacher was running a boutique in Knightsbridge and Mr Granatino working for JP Morgan on as much as £300,000 a year when the two met.

He gave up his banking career in 2003 to pursue a doctorate in biotechnology at Oxford. The couple separated in 2006 and were divorced soon after. Ms Radmacher now lives in Germany with the couple’s children.

After the ruling Ms Radmacher said in a statement: “I am delighted that the court accepts that the agreement Nicolas and I entered into as intelligent adults before our marriage should be honoured. Ultimately, this case has been about what I regard as a broken promise. When we met and married, Nicolas and I were broadly on an equal footing financially.

“He too is an heir to a multimillion-pound fortune and, when we met, was an investment banker earning up to £330,000 a year.

“The agreement was at my father’s insistence as he wanted to protect my inheritance — this is perfectly normal in our countries of origin, France and Germany. My father taught me the value of hard work and family values.

“Like all wealthy parents, he feared gold-diggers.

“As an heir himself, Nicolas perfectly understood this. The agreement gave me reassurance that Nicolas was marrying me because he loved me as I loved him. . . that we were marrying for the right reasons.

“Nicolas and I made each other a promise and all I have been asking is that he be kept to it.”

Mr Granatino is expected to seek permission to take the case to the House of Lords for the issue of prenuptials to be reviewed by the highest court in the land.

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