Cowell, 52, who works with Lovato on the US version of 'The X Factor', said he loved her really but also found her to be "very annoying", reported Femalefirst.
"She's annoying, obnoxious, disruptive, gobby, irritating, bad manners, not great taste - did I say irritating? Yes? Annoying, very annoying. She's a brat. "I could go on for hours, but that's what makes her special, and I really do love her, a bit. Have a great night, wish I was there, but no one invited me," he said.