Story highlights Tony Schwartz was a ghostwriter who worked with Donald Trump on 'The Art of the Deal'

He said Thursday that he regrets his role in building up Trump several decades ago

(CNN) Donald Trump's former ghostwriter resumed his searing criticism of the Republican nominee Thursday, describing the Republican presidential nominee as a megalomaniac who cares only about himself.

Tony Schwartz, the credited co-author on Trump's 1987 memoir "The Art of the Deal," dismissed the notion that the Manhattan businessman has another side to his personality.

"There is no second Donald Trump," Schwartz said in an interview on CNN's "New Day." "The inner Trump is the outer Trump."

Schwartz this month emerged as one of Trump's most vocal critics, while lamenting his part in creating the brash billionaire's legend.

"I put lipstick on a pig," Schwartz said in an interview earlier this month with The New Yorker . The day that interview ran, Schwartz received a cease-and-desist letter from the Trump Organization's general counsel demanding that he return all royalties made off the book.

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