Jennifer Lopez has advised Britney Spears and Demi Lovato to be true to themselves when they begin their judging roles on 'The X Factor' USA.

The 42-year-old 'American Idol' judge said that she felt "scared" for 30-year-old Britney and 19-year-old Demi because she was under a lot of pressure to impress when she started on her rival show.

She said: "Just be yourself. I think it's just about really being your true self, not trying to be something that you're not. I feel a little scared for them 'cause I was scared when I started. It's live TV - there's a lot of pressure that goes with it - but I think they'll do great.

However the singer and 'What To Expect When You're Expecting' actress - who stars as a panelist alongside Steven Tyler and Randy Jackson - believes the former Disney ladies will do well due to their experiences.

She added: ''They've both been in the spotlight since they were very young, so they'll be fine.''

Britney began her career on the 'Mickey Mouse Club' while Demi appeared in 'Sonny with a Chance.'