Billionaire Dumped Her for His New Wife — Now His Ex Is Demanding $400 Million for “Broken Promises”

The former partner of Texas oil billionaire Sid Bass has filed a federal lawsuit in New York, accusing the billionaire of reneging on promises of financial support after leaving her for another woman, according to The New York Times.

Interior designer Oona O. Sperr claims that she gave up her own career during their decade-long relationship. Bass, a billionaire who has been married three times, was previously married to two women who were prominent figures in New York’s cultural and philanthropic circles.

Bass’s first marriage, to Anne Hendricks Bass, ended in 1988. Following their divorce, Anne reportedly received at least $200 million as well as more than 1 million Disney shares owned by her husband. At the time, the settlement was considered the largest divorce payout in Texas history.

Sperr, now 64, says she was Bass’s partner from 2014 to 2024. She managed several of his townhouses on Manhattan’s Upper East Side, wore a 25-carat diamond he gave her on her ring finger and regularly appeared with him at high-profile social events, where she was variously introduced as the billionaire’s wife or partner.

But they were never legally married.

According to the lawsuit, shortly after Bass was diagnosed with Parkinson’s disease, he asked Sperr to separate. He later married Althea Irene Viafore Cress, 68.

Sperr has also named the billionaire’s new wife as a defendant. She accuses Cress of manipulating Bass, taking advantage of his deteriorating cognitive condition and actively intervening to prevent Sperr from receiving financial support.

The lawsuit puts Bass’s fortune at at least $4.4 billion.

Unlike Bass’s first two wives, who received substantial financial settlements and property after their marriages ended, Sperr has far fewer legal options because she cannot seek a divorce settlement.

Her lawsuit therefore argues that her loyalty, trust and decision to abandon her career in order to make Bass the center of her life for a decade entitle her to a comparable financial payout.

Sperr is seeking $400 million.

The Billionaire’s Long History of High-Profile Romances

The lawsuit is the latest chapter in a string of dramatic breakups in Sid Bass’s personal life.

Four decades ago, his split from his first wife became one of New York’s most talked-about social scandals of the 1980s. Bass left Anne Hendricks Bass for socialite Mercedes Kellogg after the pair were reportedly caught together at Paris’s Hôtel Plaza Athénée.

Bass later married Kellogg, a prominent philanthropist who supported the Metropolitan Opera and served as its managing director for many years.

The couple married at New York’s Plaza Hotel in 1988 — just months after Sid’s younger brother, Robert Bass, sold the famed hotel to Donald Trump for $390 million.

But that marriage also came to an end. In 2011, after 23 years together, Sid and Mercedes Bass separated.

“They Decided to Build a Life Together”

According to the lawsuit, in January 2014, Bass invited Sperr to lunch at his townhouse on East 94th Street in New York and asked her to never leave him.

“During that lunch in Manhattan, and in subsequent conversations in New York over the following days and weeks, Sid made clear, and Oona agreed, that they would build a life together,” the lawsuit states.

Sperr claims that this promise was the reason she gave up her career, believing Bass would provide for her financially.

“This is a case about broken promises,” Sperr’s attorney Roberta Kaplan said.

According to Kaplan, Bass is a billionaire worth at least $4.4 billion, while Oona “spent ten years devoted to making Sid’s life comfortable.”

Her attorney said Sperr “had no choice but to turn to the courts.”

He Promised Her $50 Million

Sperr claims she had no idea for much of their relationship that Bass was romantically involved with Cress. She says she was therefore stunned when, in September 2024, he told her he wanted to end their relationship and asked her to move out.

Bass allegedly offered Sperr a $50 million lump-sum payment, according to the lawsuit. He also allegedly promised to give her a home in New York as well as another property of her choosing.

Sperr further claims that Bass promised to continue paying for the care of her mother.

But less than a month later, she received a letter from the billionaire’s attorneys titled “Maintenance Agreement.”

Instead of the promised $50 million upfront, she was offered payments of $5 million a year for 10 years.

Sperr argues that the arrangement significantly reduced both the security and the real value of the payments, effectively forcing her to “become entirely dependent on Sid’s increasingly unpredictable decisions.”

According to the lawsuit, Bass also:

• Denied her ownership of any home;
• Offered her only the right to live in a property, rather than own it;
• Reneged on his promise to pay for her mother’s care;
• Demanded that she sign a non-disclosure agreement.

By that point, the lawsuit alleges, Bass was already in a relationship with Cress.

The couple married in August 2025. Sperr says she learned of the wedding through a single six-sentence email with the blunt subject line: “News.”

Now the billionaire’s former partner is seeking $400 million in court, arguing that the decade she devoted to Sid Bass and his life should come with a price.