(Cover) - EN Showbiz - Britney Spears "really wants" to prove her worth on The X Factor US, despite feeling "out of her comfort zone".

After much speculation, Britney and fellow songstress Demi Lovato confirmed they will be joining Simon Cowell and L.A. Reid on the judging panel of the hit American TV talent show earlier this month.

There have been concerns that Britney may not be ready to return to the spotlight, after a history of emotional issues. However, sources close to the star says she is eager to prove critics wrong.

"She's fragile, but Simon knows what he's doing - she lights up on camera," an insider told British magazine Closer. "Britney might be out of her comfort zone now, but once the anxiety fades she'll be amazing.

"She really wants this - although Simon admits it's been a nightmare keeping her happy!"

Simon recently defended his decision to sign Britney, insisting he was "not at all" worried about how the 30-year-old star will handle being on live TV.

Britney has been preparing for her turn on the hit series, enlisting in a "beauty boot camp" to ensure she's looking and feeling her best.

"She's looking tons better and feeling it too. They imposed a strict bedtime for one thing - Brit had a tendency to stay up all night on YouTube or watching movies," a source added. (C) Cover Media