A businessman who lives in London and is worth millions installed another woman into his home and asked his partner of 30 years if she would stay on as a housekeeper, a High Court judge heard.
And the man - who has interests in a portfolio of property in London - could not understand why his partner "through her lawyers" became "so aggressive", said Mr Justice Bodey.
Detail emerged as the partner was awarded a payout of more than £6 million by the judge after the couple fought over money at a hearing in London.
Mr Justice Bodey ruled that she was entitled to nearly half of a "kitty" containing more than £13m.
The judge had analysed arguments over how much the partner should get, following the breakdown of the relationship, at a private trial in the Family Division of the High Court.
He said his judgment could be reported but said the couple, from London, could not be identified.
Mr Justice Bodey said the man was in his 70s and the partner in her 50s.
They married in the late 1970s and divorced in the 1990s. But the judge said they treated the divorce as "just a piece of paper" and carried on living together.
About five years ago the man met another woman.
"The husband installed the other woman - and her 12-year-old daughter - into the marital home," said Mr Justice Bodey.
"The husband told (his partner) he was not intending her to vacate and would she remain as some sort of housekeeper?"
He said she found the suggestion "very demeaning and upsetting" and consulted solicitors.
But the man told her that he would "commit suicide or go on hunger strike" if she "went to court regarding financial matters".
Mr Justice Bodey said litigation started and added: "He could not come to terms with why (the partner), through her lawyers, had become so aggressive."
The judge concluded that there was "no distinction" between the couple's marriage and their life together after the divorce.
He said the couple, who had no children, were in a relationship spanning three decades.
He ruled that the partner should get £6.12m of a £13.6m fortune.
The man had argued that he and his partner reached an agreement which meant that she would be entitled to no more than £3.4m.
His partner said the agreement was signed after she was placed under duress.
He denied the allegation but the judge ruled in the partner's favour.