President Trump’s personal lawyer Rudy Giuliani slammed John Bolton in a new interview, describing him as a “backstabber” and rejecting claims about the commander-in-chief allegedly made by the former national security adviser in his tell-all book.

“[Bolton] never said to me, ‘I’ve got a problem with what you are doing in Ukraine,'” Giuliani told CBS News in an interview airing Wednesday, “ever once, never winked, never sent me a little note. He is a personal friend, I thought.”

“So here’s the only conclusion I can come to, and it’s a harsh one, and I feel very bad about it: He’s a backstabber.”

Giuliani, who finds himself a key player in the Ukraine scandal at the heart of Trump’s impeachment, continued to unload on the man he referred to as a “friend.”

“If your friend was complaining about you behind your back and didn’t have the guts to come up to your face and tell you, ‘I think you’re screwing up’ … that’d be a backstabber. That’s classic backstabber. So I feel I got a swamp character here,” the former New York City mayor griped.

During his final months in the Trump administration, Bolton became incensed after learning that Giuliani, along with two other administration officials, had begun conducting shadow foreign policy to pressure Ukraine to open investigations into former Vice President Joe Biden and his son Hunter, according to testimony by former National Security Council (NSC) Senior Director Fiona Hill to House impeachment investigators.

Bolton was so disturbed that he instructed Hill, who reported to him, to keep tabs on the situation and deliver her findings to the NSC’s chief lawyer.

Hill told the House that Bolton referred to Giuliani as a “hand grenade who’s going to blow everybody up.”

As the Ukraine pressure campaign by Giuliani and others ramped up, Hill testified, Bolton ordered her to go speak with White House lawyer John Eisenberg.

Hill added that Bolton told her to tell Eisenberg, “I am not part of whatever drug deal [US Ambassador to the EU Gordon] Sondland and [acting White House chief of staff Mick] Mulvaney are cooking up.”

Giuliani’s interview marks the first time he has spoken about Bolton since that testimony was made publicly.

Giuliani was quick to dismiss claims made by Bolton in his upcoming book.

“I find his testimony about the president pretty close to incredible. I can’t imagine that the president of the United States said that to him.”

Earlier this week, portions of Bolton’s book were leaked to the New York Times, specifically including claims Trump told Bolton during an August 2019 meeting that the withholding of military aid to Ukraine was tied to investigations into Democrats.

Following the leak of the manuscript, Trump took to Twitter to deny the claims.

Trump is undergoing an impeachment trial in the Senate over his alleged withholding of the critical military aid and a White House meeting for Ukraine in exchange for the announcement of an investigation into Joe Biden, his chief political rival in the 2020 election.

Bolton has been viewed as a key witness for the Democrats’ case against the president. Earlier this month, the former national security adviser said he would testify if subpoenaed by the Senate.