President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE made "a rare admission" of regret to aides after sending then-White House press secretary Sean Spicer Sean Michael SpicerKellyanne Conway to leave White House at end of month Pro-Trump duo Diamond and Silk launch new program on Newsmax TV The Hill's 12:30 Report - Presented by Facebook - Supreme Court's unanimous decision on the Electoral College MORE to fight with the press over reports detailing the crowd size as his Inauguration Day ceremony, according to a new White House tell-all.

Fox News host Howard Kurtz described the incident in his new book, “Media Madness: Donald Trump, The Press, And The War Over The Truth.”

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Special counselor Kellyanne Conway Kellyanne Elizabeth ConwayGeorge and Kellyanne Conway honor Ginsburg Trump carries on with rally, unaware of Ginsburg's death George Conway hits Trump on 9/11 anniversary: 'The greatest threat to the safety and security of Americans' MORE initially tried to persuade the president against the idea of sending Spicer out in his defense, according to an excerpt, as reported by The Washington Post.

She appeared to be one of the few who could calm Trump down, according to the book, using a line she regularly employs with the president when he gets irritated about a matter: "You’re really big. That’s really small.”

But Spicer ultimately came to the podium swinging during his first official White House news conference, insisting that the audience in attendance was larger than for former President Obama.

Spicer inaccurately claimed a day after the inauguration that Trump had “the largest audience to ever witness an inauguration, period, both in person and around the globe.”

The statement created a dizzying distraction for the White House early in the administration.

Kurtz says following the news conference, Trump make “a rare admission” that he had been wrong. “You were right. I shouldn’t have done that,” he told aides, according to the book.

Spicer told HLN earlier this month that his claim about the crowd size on Trump's Inauguration Day is "first and foremost" an example of one of the times he "screwed up" while serving as the White House mouthpiece.

Spicer left his White House post in August.