The highest court in the land has ruled in favour of heiress Katrin Radmacher, giving new status to pre-nuptial agreements.
Nicolas Granatino, husband of the German heiress said to be worth more than £100 million, took the case to the Supreme Court after appeal judges slashed his divorce settlement from more than £5 million to £1 million.
Appeal judges had ruled that "decisive weight" should be given to the agreement signed before he married that he would make no claims on Katrin Radmacher's fortune.
The case was seen by lawyers as the ultimate test of whether the agreements are applicable in English law.
Nicholas Mostyn QC, representing Mr Granatino, had told the nine justices headed by Lord Phillips at a hearing in March that the Court of Appeal ruling was not only unfair, it was impermissible because it amounted to a court legislating over pre-nuptial agreements which are not recognised in English law.
By a majority of eight to one, the justices dismissed the ex-husband's appeal, saying that following their ruling "it will be natural to infer that parties entering into agreements will intend that effect be given to them".
Katrin Radmacher, who was present at the Supreme Court for the ruling, said afterwards: "I am really pleased with the ruling but saddened at the four-year process that brought us to this point. I am delighted that Britain has upheld fairness. It is important to me that no-one else should have to go through this."
In a statement, Ms Radmacher said: "For Nicolas and I, in our homelands - France and Germany - these agreements are entirely normal and routine. We made a promise to each other that if anything went wrong between us, both of us would walk away without making financial claims on each other.
"The promise made to me was broken. I know some people think of pre-nuptial agreements as being unromantic, but for us it was meant to be a way of proving you are marrying only for love.
"It was a natural part of the marriage process. In my case, my father insisted upon it to protect my inheritance. Sadly it has taken four years to have our agreement upheld in the British courts. I'm so relieved it's over."