Lawyers for one billionaire financier who’s suing to stop his ex-wife from taking half of his assets have hit on a novel strategy for winning their case: Proving that the couple were never married in the first place.

Asif Aziz, founder and chief executive officer of the real estate investment company Criterion Capital Ltd., says he was never married to Tagilde Aziz under English law, in a case that could be one of the largest divorce cases in UK history.

The lawsuit was filed in Asif’s hometown of London, according to Bloomberg.

In their rebuttal, lawyers for Tagilde - who shares four children with Aziz – argue that, while they were never legally married, Tagilde was “presented to the world” as Asif’s wife and is seeking a “fair share” of his wealth, which she values at 1.1 billion pounds ($1.3 billion).

Funds overseen by Criterion investments, Asif’s firm, have invested in the Trocadero entertainment complex in London’s Piccadilly Circus, according to its website, and its most recent accounts show its revenue in the year to March 31, 2016, was 4.3 million pounds.

Ultimately, the dispute will likely turn on whether Asif’s lawyers can prove that two ceremonies held in Malawai in 2002 and in Wimbledon in 1997 constituted legally binding weddings.

Tagilde Aziz says she was already pregnant when they held a “nikah,” a type of religious ceremony, in South London at the insistence of family. She says she hadn’t divorced her first husband at the time.

Five years later, she says they had another ceremony at the home of his uncle in the African country with a “lavish feast.” Tagilde is also alleging that Asif has tried to intimidate her, in part by being the “puppet master” behind “ferocious litigation” that she faces in the UK and Gibraltar.

The ultimate ruling on whether the couple was married will be a big factor in Tagilde Aziz’s final recovery.

“If he were able to satisfy a court that they were not married, the wife would still get something but it would probably be substantially reduced,” said Graham Coy, a London divorce lawyer who isn’t involved in the case.

Asif, for what it’s worth, is claiming he is worth far less, with his lawyers arguing that he earns a meager 400,000 pounds a year. Court documents prepared for Wednesday’s hearing on behalf of Tagilde Aziz said Asif Aziz had argued that “he has no capital, is a man of straw and has accumulated debts as a result of these proceedings in excess of 600,000 pounds.”