President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE’s attorney Rudy Giuliani lashed out at Trump’s former longtime personal lawyer Michael Cohen on Thursday night, questioning his credibility and calling him a "pathological liar."

Giuliani ripped into Cohen during an appearance on CNN's "Cuomo Prime Time" after the network reported on Cohen's claims that Trump had advance knowledge of a 2016 Trump Tower meeting between Trump campaign officials and a Russian lawyer.

“He’s been lying all week, he’s been lying for years,” Giuliani said of Cohen.

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Earlier this week, CNN aired audio from a 2016 conversation between Cohen and Trump about a payment tied to a former Playboy model alleging an affair with Trump. Cohen had secretly recorded the conversation, which is one of several tapes currently in the possession of federal investigators.

“The tapes that we have demonstrate any number of very serious lies back a year and a half ago, including his fooling people, hiding tape recordings, telling them they aren’t recorded, lying to their face, breaking faith with them,” Giuliani said of Cohen on CNN. “I don’t see how he has any credibility.”

“He has lied all his life… a person who is found to be an incredible liar, he’s got a tremendous motive to lie now… I don’t think anyone believes that.” Rudy Giuliani dismisses report Michael Cohen claims Trump knew in advance of 2016 Trump Tower meeting https://t.co/xd4PFYYpcQ pic.twitter.com/9gxjNGWLRA — Cuomo Prime Time (@CuomoPrimeTime) July 26, 2018

CNN reported minutes earlier that Cohen is willing to tell special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE that Trump approved the Trump Tower meeting between Russian lawyer Natalia Veselnitskaya and Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE, among other Trump campaign officials.

Trump, Trump Jr. and others have all denied that the president knew about the meeting before The New York Times revealed the meeting's existence in July 2017.

“There’s nobody that I know that knows him who hasn’t warned me that if he’s backed up against a wall he’ll lie like crazy, because he’s lied all his life,” Giuliani said of Cohen on Thursday.

He added that Cohen is “the kind of witness who can really destroy a whole case.”

“A person who is found to be an incredible liar, he’s got a tremendous motive to lie now because he’s got nothing to give, says it, all of a sudden, at the 11th hour. I don’t think anybody believes that,” Giuliani said.

Giuliani also said he has spoken with the other people in the room during the meeting that Cohen was referring to, claiming that they can corroborate that Trump Jr. did not discuss the Trump Tower meeting with his father.

Cohen is under federal investigation by prosecutors in New York, and reportedly believes telling Mueller his account of the meeting with Trump will alleviate some of the pressure from the probe, CNN reported.