In an extensive interview with The New Yorker, the ghostwriter for Donald Trump’s best-selling book “The Art of the Deal” describes the presumptive GOP nominee as “impatient,” “irritable” and untrustworthy. He also says he regrets helping write the book — and the millions of dollars that came with it.

Tony Schwartz co-authored “Trump: The Art of the Deal” in 1987. The book spent 13 weeks atop the New York Times best-seller list and has sold millions of copies in the decades since its release.

Though he got half of the book's advance and half the royalties, Schwartz says he now regrets his work on the book.

“I put lipstick on a pig,” Schwartz said in The New Yorker piece. “I feel a deep sense of remorse that I contributed to presenting Trump in a way that brought him wider attention and made him more appealing than he is.”

Schwartz describes Trump as difficult to work with, especially for long periods of time. At one point during the process of writing the “Art of the Deal,” Schwartz says was forced to change his interview style to accommodate Trump’s attention span.

“If he had to be briefed on a crisis in the Situation Room, it’s impossible to imagine him paying attention over a long period of time,” he said.

Schwartz also claims he didn’t fully investigate Trump’s business dealings and whited out unflattering details of the businessman's past dealings.

Finally, Schwartz says that after throwing an elaborate book release party at Trump Tower, Trump asked his ghostwriter to split the party’s six-figure cost.

"I genuinely believe that if Trump wins and gets the nuclear codes there is an excellent possibility it will lead to the end of civilization,” Schwartz told The New Yorker.

Read the entire piece from The New Yorker here.

Alex Hider is a writer for the E.W. Scripps National Desk. Follow him on Twitter @alexhider.