White House chief of staff John Kelly reportedly once said he would have taken a "resignation letter and shoved it up" President Donald Trump's "ass six different times."

The remark was recounted in a new book by Washington Post journalist Bob Woodward, titled "Fear: Trump in the White House."

Kelly was reportedly speaking to Trump's then-economic adviser Gary Cohn, who tried to resign over Trump's approach to a white-supremacist rally in Charlottesville, Virginia, last summer.

White House chief of staff John Kelly was reportedly so furious over President Donald Trump's reaction to a white-supremacist rally in Charlottesville last summer, he once said he would have taken a "resignation letter and shoved it up his ass six different times."

Kelly's comment is recounted in a new book titled "Fear: Trump in the White House" by Washington Post journalist Bob Woodward, based on hundreds of hours of interviews Woodward conducted with people on condition of anonymity. The Post summarized Woodward's book in an article on Tuesday.

Kelly made the remark about the resignation letter to Trump's former top economic adviser, Gary Cohn, whom Trump had talked out of quitting, according to Woodward.

During internal White House meetings, Kelly made little secret of his disdain for Trump's intellect, according to Woodward. Since taking the job as chief of staff, Kelly has reportedly called Trump "unhinged," an "idiot," and told fellow staffers, "This is the worst job I've ever had."

Woodward recounted one small meeting where Kelly said it was "pointless to try to convince [Trump] of anything. He's gone off the rails. We're in Crazytown. I don't even know why any of us are here."

Kelly has even reportedly threatened to resign multiple times but never went through with it, Woodward wrote.

During Kelly's discussion with Cohn over the resignation letter, the men had reportedly been discussing their revulsion at the way Trump handled the aftermath of the violent rally in Charlottesville, Virginia, which left one woman dead.

Trump initially gave a widely criticized speech, in which he said there were "very fine people on both sides." But according to Woodward, when Trump gave a follow-up speech denouncing white supremacists and neo-Nazis, he called it the "worst speech I've ever given."

"That was the biggest f---ing mistake I've made," Trump reportedly said.

In response to the allegations in Woodward's book, White House press secretary Sarah Huckabee Sanders said the book was merely "fabricated stories" from "disgruntled employees."

Kelly said in another statement that it's untrue he called Trump an "idiot."

He continued: "As I stated back in May and still firmly stand behind: 'I spend more time with the President than anyone else, and we have an incredibly candid and strong relationship. He always knows where I stand, and he and I both know this story is total BS. I'm committed to the President, his agenda, and our country. This is another pathetic attempt to smear people close to President Trump and distract from the administration's many successes.'"