Demi Lovato thinks fatherhood has melted Simon Cowell's cold heart.

The singer joked that her fellow 'X Factor' USA mentor has been less mean-spirited on the judging panel this year, and believes the impending arrival of his first child with New York socialite Lauren Silverman might have something to do with it.

Demi quipped: ''He's [mostly] the same, but maybe he's gotten a little nicer this year.''

The 'Made in the USA' hitmaker is enamoured with new panellists Kelly Rowland and Paulina Rubio - who have replaced Britney Spears and L.A. Reid - and says the dynamic between the foursome is already proving to be more fun this season, with all three girls teaming up against head judge Simon.

Demi said: ''This year, he's up against me and two other girls who don't put up with him. It's basically a whole panel against Simon - it's great! We're not Simon's angels - we're Simon's demons!''

The 21-year-old star thinks Latina superstar Paulina in particular was a great addition to the FOX programme as she provides so much comic relief.

She teased: ''It feels like a new and refreshed version of the show. Paulina is a firecracker! You never know what's going to come out of her mouth. Pretty much everything she says makes me laugh.''