By admin 
A former girlfriend of billionaire oil heir Sid Bass claims he backed out of financial promises made to her after he married another woman, according to a federal lawsuit filed this week.
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The 98-page lawsuit, filed in a New York federal court by Oona O. Sperr, seeks at least $400 million in damages from Bass, and also names Bass’ wife, Althea Viafora Kress, as a defendant.
Sperr, 64, and Bass, 84, were partners for roughly a decade starting in 2014, and during that time, Bass bought her a diamond ring worth $2.1 million and the couple frequently held themselves out as married, according to the lawsuit. They owned several expensive properties, including one in Fort Worth, traveled together and “spared no expense on the lavish life” they shared, attorneys wrote.
At the start of their relationship, Sperr verbally agreed to give up her interior design career in favor of managing the pair’s homes, overseeing renovations, caring for Bass and representing the couple socially, according to the lawsuit. In return, Bass allegedly agreed to provide lifetime financial support and maintenance to Sperr.
The couple were so entwined with one another that they shared the same bank account and planned their wills and end-of-life care together, according to the lawsuit.
But, as Bass’ cognition and judgment deteriorated due to “excessive consumption of alcohol and early signs of Parkinson’s,” Kress began to groom him with the aim of gaining access to his fortune, attorneys for Sperr wrote in the lawsuit.
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When the relationship between Sperr and Bass eventually ended, Bass committed to continue providing financial support, care and property to her even though they were separated, according to the suit. Ultimately, though, the promised support was altered “beyond recognition,” and some aspects were repudiated altogether, Sperr’s attorneys claim.
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The initial agreement was that, in the separation, Bass would give Sperr a $50 million lump-sum payment and two properties in New York, and continue to care for Sperr’s mother, according to the suit. In a later agreement, Bass altered the financial promise to $5 million annually for 10 years, imposed non-disclosure agreements, and proposed that Sperr remain as a tenant in one of the New York homes instead of owning the property, the lawsuit states.
In part, Sperr alleges that Kress has taken full control over Bass’ household and finances, and isolated him from lifelong friends and employees, attorneys wrote in the suit. For that, Sperr is suing Kress, alleging tortious interference with a contract.
Sperr learned of Bass’ marriage to Kress last summer in a six-sentence email that bore the subject line “news,” according to the lawsuit.
“This is a case about broken promises,” Sperr’s lawyer Roberta Kaplan told the New York Times. “Sid Bass is a billionaire at least four times over. Oona is the woman who spent a decade making Sid’s life convenient.”
Representatives for Bass declined to comment Thursday afternoon.
This story was originally published September 3, 2026 at 6:24 PM with the headline “Ex-girlfriend of Fort Worth billionaire Sid Bass sues him for $400 million.”
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