Rosie O'Donnell isn't mincing words when it comes to Donald Trump's presidential campaign.

Said O'Donnell: "It's a nightmare." She didn't elaborate, adding only, "That's my quote."

The actress-comedian and billionaire GOP contender have long exchanged barbs. But his conduct became an issue at the GOP debate in August, when Trump was asked to account for crude remarks he has made about women.

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When Trump suggested he had insulted only O'Donnell, Fox News Channel moderator Megyn Kelly corrected him.

The animosity between Trump and O'Donnell dates back years. In 2006, O'Donnell criticized him for remarks he made about a winner of his Miss USA beauty pageant, saying he had no right to be a "moral compass" for the beauty queen.

That unleashed a series of barbs from Trump, who called O'Donnell a "loser" and "slob," among other insults. In turn, O'Donnell questioned his business skills and hairstyle and compared him to a "snake oil salesman."

O'Donnell, a former co-host of "The View," made her remarks Monday while discussing a guest starring role on Wednesday's episode of Fox's drama series "Empire."