It was the most provocative allegation yet in the increasingly bitter public war between rapper Meek Mill and Philadelphia Judge Genece E. Brinkley — that the judge, whose decision to send him back to prison sparked nationwide protests, was herself under FBI investigation.

That assertion, tucked without detail inside a court filing Monday and fanned by Mill's lawyers and publicists, seemed designed to call into question Brinkley's integrity and to embolden their claim that she could not be counted on to impartially rule on his fate.

But it told only part of the story, according to three sources familiar with federal authorities' involvement in the matter.

It was Mill himself who last year pressed the FBI to investigate the judge who had repeatedly concluded that he had violated the terms of his probation, the sources say. And it was Mill who brought the short-lived review to a halt by ending his cooperation.

Agents wanted the rapper to surreptitiously record conversations with Brinkley, who he alleged had tried to extort favors from him in exchange for leniency, the sources say.

But Mill refused – and the inquiry faded away.

Separate federal law enforcement sources have confirmed that there is no active investigation into the judge.  But even a fleeting mention of the now-closed inquiry was bound to raise eyebrows in a city where a number of judges have been convicted of crimes or ousted in ethical scandals in recent years.

Now, supporters of Mill — whose legal name is Robert Williams — have made it a focal point of their effort to remove Brinkley from his case. That campaign has escalated in recent days as the 30-year-old rapper's publicity machine has circulated opposition research encouraging reporters to ask questions about Brinkley's state financial disclosure filings and other matters unrelated to Mill's probation.

In their court filing Monday, Mill's lawyers argued that Brinkley's mere knowledge of the 2016 FBI inquiry poses a conflict that should prompt her to recuse herself – even if the probe was initiated by Mill and then dragged into public view this year by the rapper's defenders.

"The existence of a federal investigation involving Judge Brinkley's conduct regarding Mr. Williams, combined with Judge Brinkley's awareness of that investigation, raises further doubt as to her ability to preside impartially," their motion said.

Mill's attorneys, Joseph Tacopina and Brian McMonagle, declined to answer questions this week about their knowledge of the 2016 probe.

All three sources who described that inquiry for the Inquirer and Daily News spoke under the condition of anonymity because they were not authorized to publicly discuss the matter.

Each said that they felt compelled to come forward because they believed that the nature, extent, and driving force behind Mill's contact with federal agents had been publicly mischaracterized – including in a widely cited report last month by Page Six, the gossip column of the New York Post, in which an unnamed source said Brinkley was the target of an ongoing probe.

The Inquirer and Daily News sources say that Mill's complaint to the FBI began after a February 2016 meeting in Brinkley's chambers during which the rapper claimed the judge made a number of inappropriate requests.

The transcript of their conversation has been sealed since last year at the request of Mill and his then-lawyer Frank DeSimone.

But Tacopina has alleged in court filings that during the meeting Brinkley urged Mill to drop his current management company, Jay-Z's Roc Nation, and return to Philadelphia-based Charles "Charlie Mack" Alston, who worked with Mill earlier in his career. She also asked Mill to record a cover of a Boyz II Men song and to mention her name in it, Tacopina has said.

The agents who asked Mill to record conversations with the judge in 2016 had hoped to corroborate the rapper's claims about what he believed to be Brinkley's attempt to extort him, the sources familiar with the inquiry say.

Mill has rapped in the past that he's no snitch, including in a 2013 track "Heaven or Hell:" Before I snitch y'all gotta burn a hole in my tongue. His refusal to tape the judge brought an end to the federal probe, the sources say.

It remains unclear what other steps – if any – agents might have taken to investigate the matter before Mill ended their cooperation.

Brinkley has not responded to the rapper's claims regarding their February 2016 in-chambers conference or his lawyers' efforts to oust her based on the FBI inquiry —  a recusal request on which she herself must rule.

Mill, meanwhile, remains incarcerated in a state prison in Chester, serving the two-to-four-year sentence Brinkley imposed last month for repeated violations of his probation on a 2008 drug and gun case.

The judge has denied him bail while his lawyers continue to appeal her decision to the Pennsylvania Superior Court.