Christina Estrada, 53, who has appeared in the Pirelli calendar and was once linked to Britain's Prince Andrew, will be able to seek a share of Sheikh Walid Juffali's estimated £4 billion (five billion euro, $5.7 billion) fortune.
Juffali had argued that his status since 2014 as permanent representative for Saint Lucia to the International Maritime Organization (IMO) meant he was immune from a claim.
But at the High Court, judge Anthony Hayden ruled that argument was "spurious".
"I am satisfied that what has transpired here is that (Juffali) has sought and obtained a diplomatic appointment with the sole intention of defeating (Estrada's) claims consequent on the breakdown of their marriage," the judge added.
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Juffali is expected to appeal against the decision.
The sheikh divorced Estrada in Saudi Arabia and says he has bought her a property in Beverly Hills in the United States and pays her $100,000 (90,000 euros) a month.
But Estrada alleges she was divorced without her knowledge and cannot bring a financial claim against him in Saudi Arabia. She also claims her husband is a permanent resident of Britain.
London is increasingly seen as the divorce capital of the world, with the High Court hearing a string of cases in recent years involving wealthy couples from China, Russia, the United States and Malaysia.
Lawyers say England is seen as an attractive destination for wives seeking to divorce their husbands as awards are significantly higher than in other places.