Simon Cowell: 'Demi Lovato is irritating'

The music mogul - who works with Demi on the US version of 'The X Factor' - claimed he loved her "really" but also found her to be "very annoying" and berated the event for not inviting him.

He quipped: "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."

However, Demi hit back, claiming he was too "old" to understand women who spoke their mind.

She said: "He's just old. He isn't used to women in this century being able to say what they want."

Despite the fun, there was also time for reflection in the show at Los Angeles' Gibson Amphitheatre, as Demi dedicated a performance of her hit 'Skyscraper' to the victims of the shooting that took place at a midnight screening of 'The Dark Knight Rises' in Aurora, Colorado, last week.

Stopping mid-way through the song, she said: "It's really heavy on my heart today. A lot of you know what happened in Colorado at midnight last night. I just want to make sure we can get through this. And my heart goes out to Colorado - this song is for them."

Taylor Swift was the big winner on the night taking home five awards, narrowly beating Justin Bieber who won four prizes.