Gary Byrne says he was posted outside Bill Clinton's Oval Office in the 1990s and that what he saw 'sickened him'.
His expose is causing deep concern in the White House, according to Drudge Report, and its release comes as Hillary comes within touching distance of securing the Democratic nomination.
The book titled Crisis of Character: A White House Secret Service Officer Discloses His Firsthand Experience with Hillary, Bill, and How They Operate is set to hit shelves on June 28.
The Democratic convention, where Hillary could be confirmed as the nominee, will take place a month later.
According to Drudge, specific details of the book are being kept under a tight embargo.
A description of the book reads: 'Posted directly outside President Clinton's Oval Office, Former Secret Service uniformed officer Gary Byrne reveals what he observed of Hillary Clinton's character and the culture inside the White House while protecting the First Family.