A former Secret Service agent writes in a new book that Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE’s “Jekyll and Hyde” temper at times resulted in wild outbursts.

Gary Byrne says the likely Democratic nominee is too “erratic, uncontrollable and occasionally violent” for the presidency, according to excerpts obtained by Page Six.

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“What I saw in the 1990s sickened me,” Byrne writes in the introduction of “Crisis of Character: A White House Secret Service Officer Discloses His Firsthand Experience with Hillary, Bill and How They Operate.” The book, due out June 28, already holds the top spot on Amazon's best-seller list.

“Hillary Clinton is now poised to become the Democratic nominee for president of the United States, but she simply lacks the integrity and temperament to serve in the office,” he said.

“From the bottom of my soul I know this to be true. And with Hillary’s latest rise, I realize that her own leadership style — volcanic, impulsive, enabled by sycophants and disdainful of the rule set for everyone else — hasn’t changed a bit.”

Byrne recounted seeing a vase "smashed to bits" and Bill Clinton William (Bill) Jefferson ClintonDolly Parton remembers Ginsburg: 'Her voice was soft but her message rang loud' Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Calls grow for Biden to expand election map in final sprint MORE sporting a "real, live, put-a-steak-on-it black eye" one morning in 1995 after a loud fight between the Clintons the night before.

Clinton’s campaign on Sunday dismissed Byrne’s account, saying his new book is an attempt at profiting off the former first family.

“Gary Byrnes joins the ranks of Ed Klein and other ‘authors’ in this latest in a long line of books attempting to cash in on the election cycle with their nonsense,” spokesman Nick Merrill said. "It should be put in the fantasy section of the book store.”