FBI Director Kash Patel discovered bags filled with classified documents hidden deep inside bureau headquarters — including a secret annex to the 2023 Durham report that was never supposed to see the light of day.

According to a source familiar with the findings, Patel uncovered multiple “burn bags” stuffed with thousands of documents dating back to the FBI’s 2016 Trump-Russia investigation, code-named Crossfire Hurricane. One of the most explosive documents was found inside what is being called a secret room in the Hoover Building, the New York Post reported.

That document is a classified 29-page appendix to Special Counsel John Durham’s report on the origins of the Russia probe. Fox News Digital first reported on the discovery.

Burn bags are supposed to hold classified material that is scheduled for destruction. It’s unclear whether the documents Patel found had missed their destruction date or were being preserved intentionally.

The classified annex is now being prepared for declassification and will be handed over to Senate Judiciary Chair Chuck Grassley for public release, a source told the New York Post. Grassley’s office has not said when the release might happen.

The annex reportedly includes evidence that foreign intelligence sources warned U.S. officials that the FBI was planning to push a false narrative that Donald Trump’s 2016 campaign had colluded with the Kremlin — before the investigation even officially began.

Those reviewing the materials alongside Patel include CIA Director John Ratcliffe, Director of National Intelligence Tulsi Gabbard, Attorney General Pam Bondi, and acting NSA Director William Hartman.

President Trump addressed the discovery on Wednesday.

“I want everything to be shown,” he said. “You know, as long as it’s fair and reasonable, I think it will be shown.”

The Crossfire Hurricane investigation led to the Mueller report in 2019, which found links between Trump associates and Russians but no evidence of a criminal conspiracy. But years later, Durham concluded the probe never had a valid basis in the first place.

Durham’s findings confirmed what Patel and then-Rep. Devin Nunes had started to uncover as early as 2017. Patel was the lead investigator for Nunes’ House Intelligence Committee probe into the origins of the Russia hoax.

Patel gave a preview of the discovery last month during an appearance on the Joe Rogan podcast.

“When I first got to the bureau, [I] found a room that [former FBI Director James] Comey and others hid from the world in the Hoover Building, full of documents and computer hard drives that no one had ever seen or heard of,” he said. “They locked the key and hid access and just said, ‘No one’s ever gonna find this place.’”

Meanwhile, earlier this month, Director Gabbard made headlines of her own by releasing evidence of what she called a “treasonous conspiracy” by Obama officials to undermine Trump before he even took office.

Gabbard’s documents show the Obama administration was ready to conclude that Russia had not influenced the 2016 election — until Comey’s FBI overruled them.

In an op-ed published Wednesday by The New York Times, former CIA Director John Brennan and former DNI James Clapper pushed back, calling Gabbard’s claims “patently false.”

They admitted that Russia did not change vote totals, but said Moscow still influenced voter opinions.

“The real politicization is the calculated distortion of intelligence by administration officials, notably Mr. Trump’s directors of national intelligence and the CIA, positions that should be apolitical,” Brennan and Clapper wrote.

They added, “We find it deeply regrettable that the administration continues to perpetuate the fictitious narrative that Russia did not interfere in the 2016 election.”