George Papadopoulos, a former Trump campaign aide who has alleged that he was targeted in FBI’s Russia probe as part of a scheme to take down his boss, filed paperwork Tuesday to run for the House seat being vacated by Democratic California Rep. Katie Hill.

Papadopoulos will formally announce his run on Thursday, a general campaign consultant told Fox News' "The Ingraham Angle."

This past Sunday, Papadopoulos tweeted: “I love my state too much to see it run down by candidates like Hill. All talk, no action, and a bunch of sellouts.” Then, on Monday: "Announcement soon on my interest in Katie Hill’s soon to be vacant seat in the 25th district!"

Hill, whose district covers Los Angeles County, announced her resignation Sunday amid an ethics probe into allegations she had an inappropriate relationship with a congressional staffer and the emergence of embarrassing personal photos.

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She’s admitted to a consensual relationship with a campaign staff member, but denied one with her legislative director, which would violate U.S. House rules. She’s also called herself the victim of revenge porn by an abusive husband she's divorcing.

Hill has also said the right-wing media took her down.

Papadopoulos was a key figure in the FBI’s Russia probe into ties between Russia and the Trump campaign. That investigation began after revelations that Papadopoulos had learned in 2016 from Maltese professor Joseph Mifsud that Russia had “dirt” on Democratic presidential candidate Hillary Clinton in the form of thousands of emails.

He then used that connection to try to set up a meeting between President Trump, then a Republican presidential candidate, and Russian President Vladimir Putin.

Although Special Counsel Robert Mueller's probe has concluded, Papadopoulos has remained in the headlines. A source in the Italian Ministry of Justice told The Daily Beast earlier this month that Attorney General Bill Barr and U.S. Attorney John Durham, who are investigating possible FBI and DOJ misconduct during the Russia probe, were played a taped deposition made by Mifsud.

Mifsud reportedly was explaining to investigators in the deposition why people would want to harm him, and why he needed police protection. Papadopoulos has suggested he was connected with Mifsud as part of a setup orchestrated by intelligence agencies.

In July, Papadopoulos told Fox News' Maria Bartiromo in an exclusive interview that he was heading back to Greece to retrieve $10,000 that he suspects was dropped in his lap as part of an entrapment scheme by the CIA or FBI -- and federal investigators want to see the marked bills, which he said are now stored in a safe.

Papadopoulos pleaded guilty to lying to the FBI and cooperated in Mueller’s investigation. He was sentenced in fall 2018 to 14 days in prison.

He enters a field of at least three other Republicans and one Democrat. The other Republicans are Navy veteran Mike Garcia, bank executive Angela Jacobs Underwood and Mark Cripe, who works for the Los Angeles County Sheriff’s Department. Former Republican Rep. Steve Knight, who lost the seat to Hill in 2018, is also considering running.

The seat was the last Los Angeles County seat to be held by Republicans before Hill’s victory and was one of seven Democrats flipped last year.

State Assemblywoman Christy Smith is the only Democrat in the race so far. She quickly criticized Papadopoulos on Tuesday.

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“If he pled guilty to lying to the FBI -- how do we know he’ll tell us the truth?” Smith tweeted. “We deserve someone from our community serving as our voice -- not (Trump’s) wannabe political hack!”

"The Ingraham Angle" producer Ali Holston and The Associated Press contributed to this report.