It was the billion-dollar breakup.

The 2016 Republican presidential primary left scores of relationships frayed and hobbled. The most consequential—at least, from a financial perspective—is likely the breakdown between Manhattan billionaire hedge fund heiress Rebekah Mercer and the new-money self-made fracking billionaire brother duo Dan and Farris Wilks.

Back in early 2015—it feels like a lifetime ago!—an ally of Sen. Ted Cruz’s team announced that a super PAC franchise had locked up more than $30 million to back the Texan, primarily from three wealthy conservative families.

But with extraordinary amounts of money came white-hot tension. At the heart of the tension was Breitbart News, the site’s top funder, its chief executive, and the intensifying feud between then-Republican presidential frontrunner Donald Trump and his chief primary rival. Multiple sources now tell The Daily Beast that the resulting fallout could have an impact on the company’s future.

Jon Francis, the Wilks brothers’ son-in-law who was involved in the super PAC expenditures, disputed some of this: He said in an email that any tension between the families was solely a result of disputes over Breitbart’s coverage of the race and that the Wilkses have nothing but respect for the Mercers despite those disagreements.

Rebekah Mercer and her attorney did not respond to requests for comment.

BREITBART VS. THE BILLIONAIRES

This all started on April 8, 2015, when a Cruz ally told Bloomberg that a franchise of super PACs backing his presidential bid had amassed a whopping $31 million. It soon emerged that those super PACs, called Keep the Promise 1, Keep the Promise 2, and Keep the Promise 3, were funded by Robert and Rebekah Mercer; Farris and Dan Wilks; and Toby Neugebauer, the son of former Texas Rep. Randy Neugebauer.

The innovative three-part structure meant each donor family had maximum control over how their millions got spent.

At the time, Rebekah Mercer had an ownership stake in Breitbart, which she holds today. She has leveraged that stake in the company to force out former White House chief strategist Steve Bannon, who has led Breitbart since 2012, with a brief sabbatical to serve on the Trump campaign and in a senior position in the Trump White House.

Mercer and Bannon had a very public falling-out last week over the latter’s published comments in a salacious new book about the Trump White House. But two years ago, Mercer was far more forgiving of her political consiglière—despite complaints from allies in the pro-Cruz effort who complained Bannon was throwing a wrench in the works.

In the final months of the Republican primary, Breitbart began running stories giving credence to Trump’s most eye-popping criticisms of Cruz. The site repeatedly fueled speculation that Cruz was ineligible to serve in the White House because he was born in Canada and gave oxygen to Trump’s speculation that Cruz’s father was complicit in the assassination of John F. Kennedy.

The stories put Rebekah Mercer in an awkward situation: The news website she funded was vociferously—and conspiratorially—bashing the candidate she also funded.

Jon Francis, the Wilks brothers’ son-in-law, was advising them at the time on their political spending. He wasn’t impressed with Mercer’s business acumen, according to a Republican operative familiar with his thinking, and he wasn’t coy about it.

Over the tense weeks when the Republican primary came down to Cruz versus Trump, Francis criticized Mercer in a way she found insulting, per that same operative, suggesting she lacked business acumen and couldn’t keep her people in line. He also said he would never let a company he owned get away with doing what Breitbart was doing to Cruz.

“There was a lot of butthurt to go around,” said one Texas Republican operative familiar with the situation.

Francis told The Daily Beast in an emailed statement that there “simply isn’t any truth” to claims that the bad blood between the families persists to this day.

“My family has nothing negative to say about the Mercers,” he said.

He didn’t dispute they had disagreements that grew tense.

“It became apparent to me that Breitbart News was running interference for the Trump campaign,” Francis said. “I didn’t want Breitbart to run interference for us or to turn against Donald Trump. I just wanted them to function like a news site and not like an arm of the Trump campaign, which is how I saw them.”

Francis said in the email that he confronted Mercer about Breitbart’s covert support for Trump and that she dismissed his concerns.

“She felt that Breitbart was just calling it as they saw it,” he said. “I told her I thought she was missing something that was becoming obvious to everyone else, and that I believed Steve Bannon was actively currying favor with Trump. She stood her ground.”

“It wasn’t a fight. It wasn’t part of any broader conflict,” he said. “It was a disagreement between two passionate people in a stressful situation. After that, we got back to work.”

Both families kept working with the super PAC until Trump’s victory in the Indiana primary ended Cruz’s bid.

But well-placed sources say the “butthurt” between the two families didn’t dissipate. Instead, the Keep the Promise mess left a rift between the Wilks family and the Mercers—one that plugged-in sources suspect will be irreversible.

One contributing factor was cash. Initially, the Wilks brothers, the Mercers, and Neugebauer each committed to spend $10 million on their individual Keep the Promise franchises.

But that’s not what happened. By the time Cruz conceded the primary, the Mercers had dropped $13.5 million boosting the Texan, and another $2 million after the primaries ended. The Wilks brothers had donated $15 million, but more than $8 million was refunded to them after Cruz withdrew from the race. Neugebauer, meanwhile, chipped in $10 million and had nearly $9 million refunded the day after Cruz ended his campaign, according to FEC filings.

Neugebauer’s unspent money left the other families irate.

“That was the common bond: everybody venting about Toby disappearing,” said a Republican operative.

Despite that shared ire, the Republican operative familiar with the Wilks family’s thinking told The Daily Beast it’s all but certain the two families will never again both invest in the same project.

BREITBART FOR SALE?

In addition to their political and charitable giving, the Wilkses also own the Daily Wire, an online outlet led by conservative author and pundit Ben Shapiro.

Shapiro, a former Breitbart editor, has also clashed with Bannon. And multiple sources said he has floated potentially marshalling the Wilkses’ financial support to buy Rebekah Mercer’s stake in Breitbart. But that prospect appears dim, thanks in part to the messy history between the Wilks brothers and the Mercers.

The Republican operative familiar with the Wilks family’s thinking said that as long as the Mercers are invested in Breitbart, the Wilks brothers—and, by extension, Shapiro—will stay out: eyeing Breitbart from afar, biding their time.