Before billionaire active investor Paul Singer was revealed as a financing source for the research firm that eventually produced the Trump dossier, he joked about investing in the former real estate magnate's bonds.

Singer, the founder of $34 billion hedge fund Elliott Management, apparently was a bondholder in some of Donald Trump's ill-fated business and real estate ventures. He joked with Carlyle Group (CG - Get Report) founder David Rubenstein about the matter in a sit-down with him for Bloomberg in June.

Singer, 73, said he had not met Trump ahead of the election. "I invested in his bonds, though, a couple of times," he said, garnering chuckles from the audience.

"Those were high-grade bonds?" Rubenstein asked.

"They were on the date of issue," Singer replied, to more laughter.

"They later became high-yield," Rubenstein said.

"And below," Singer added.

Trump's businesses filed for bankruptcy protection six times during his career, largely tied to his hotel and casino ventures in Atlantic City, New Jersey, and New York City. According to a report from The New York Times, Trump's casino stock and bondholders lost more than $1.5 billion throughout the ordeal.

To be sure, Trump's bonds aren't the only ones in which Singer has invested. He famously engaged in a 15-year battle with the Argentine government over Elliott's holdings in its bonds, and his fund has a significant track record in distressed debt investing. (As of late, its reputation has been tied more to activist investing.)

Singer has been caught in the crosshairs of ongoing revelations on the forces behind the set of memos on President Donald Trump and Russia. The Free Beacon, which has been in large part funded by Singer, was revealed to have first hired Fusion GPS, the research firm that later produced for Democrats the now-infamous "Trump dossier," to dig up dirt on Trump.

It's no secret Singer, a prominent Republican donor, is no fan of Trump. He supported Marco Rubio during the Republican primaries and in the summer of 2016 said he thought Trump's policies would cause a "widespread global depression."

According to the Center for Responsive Politics, Singer made more than $26 million in contributions in the 2016 election, all of which went to conservative causes -- but not Trump.

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In the Rubenstein interview, Singer reluctantly admitted he had voted for Trump but obviously remained lukewarm. "I voted for him, and there's, I was not going to vote for Hillary Clinton, as some of my Republican friends did. And I became optimistic about some of the opportunities in economic growth and regulatory reform, tax reform," he said, shrugging.

Trump in February said that Singer visited him at the White House and acknowledged that he had been "very much involved" with the anti-Trump movement. "He was a very strong opponent and now he's a very strong ally and I appreciate that," the president said at the time.

Singer in June said their meeting had to do with "taxes and economic policy."

A spokesman for Elliott declined to comment on Singer's role in the anti-Trump research and the relationship between Singer and Trump.

The Free Beacon, which Singer funded, hired Fusion GPS in 2015 to unearth information about several GOP candidates, including Trump. Eventually, funding for the project landed in the hands of Hillary Clinton's campaign and the Democratic National Committee, which later resulted in the dossier.

The Free Beacon said in a statement on Friday that it had retained "third party firms," including Fusion GPS, to provide research on "multiple candidates" but had no knowledge of the dossier.

Former Trump chief strategist Steve Bannon has "declared war" on Singer for his role in the dossier, according to a report from Axios. But it is unclear what battles lie ahead, especially in light of impending tax reform efforts. As Axios notes, Singer has already made a "major commitment" and cut substantial checks to outside groups in support of Trump's tax reform push.

"I think it's important for citizens to inform citizens, to try to give assistance," Singer said over the summer. "We're among Republican activists who actually can, in a relatively unconflicted level, we have less parochial interests in the things that we talk to policymakers about than most folks."

Correction: Story corrected to list Singer as financing source of the research firm that later produced the dossier. Story originally cited him as financing source of the research.

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Editors' pick: Originally published Oct. 31.