A millionaire told to pay his ex-wife £48m is challenging the divorce settlement in the Appeal Court, claiming his £20m offer was adequate.
John Charman said last year's High Court ruling was "unreasonable"
The High Court award made to Beverley Charman last year was thought to be the biggest in British legal history.
At the time, lawyers for John Charman, 54, who now lives in Bermuda, said it was "unreasonable" and "unfair".
The couple split in 2003 after 27 years of marriage. Mrs Charman, 53, stayed in the family home in Kent.
The appeal hearing is expected to last three days.
Barry Singleton QC, for Mr Charman, said he wanted to make it clear that another woman was not the cause of the marriage breakdown.
He said: "The parties' relationship had become very distant as it was not until May 2003 that the husband told the wife of his move offshore, according to her, only as a result of her pressing him about it."
Mr Singleton added: "The parties come from extremely modest backgrounds. The wealth in this case has been generated by the husband's endeavours in the global insurance industry."
Mrs Charman is being represented by Martin Pointer QC, who is expected to argue the House of Lords has laid down clear guidelines on divorce cases.
Mr and Mrs Charman met at school more than 30 years ago and were married in 1976, when neither had much money.
Mr Charman went on to build up wealth in the insurance market in the City of London.
In 1987, he set up the Bermuda-based Dragon Trust, which had assets worth £68m.
Petition for divorce
He also set up Axis, a global insurance and reinsurance company, also based in Bermuda, after the 9/11 attacks in New York.
The couple had two children and lived at Dell House in Sevenoaks, valued last year at £2.75m.
But in early 2003, Mr Charman moved permanently to Bermuda and separated from his wife who remained in England.
She issued a petition for divorce in June 2004.
In the High Court, Mr Justice Coleridge previously found assets in the case amounted to just over £131m including trust assets.