Simon Cowell has reportedly offered Beyonce Knowles $500 million to be a judge on US 'X Factor'.

The music mogul is thought to be keen on acquiring the 'Single Ladies' hitmaker's services for five series as he searches for a "big name" celebrity to replace axed former judges Nicole Scherzinger and Paula Abdul in order to improve the Fox show's ratings.

A source told MediaTakeout.com: "He wants a big name female star on the panel. Mariah [Carey] is good, but she's not that hot today.

"He wants Beyonce because that would immediately give him the bounce needed to beat 'American Idol'."

Meanwhile, Randy Jackson thinks Mariah would be an "amazing" US 'X Factor' judge and he hasn't ruled out the possibility of her joining the show.

The 'American Idol' panellist - who manages the 'Hero' singer - told reporters: "She'd be amazing. I mean, I manage her, so of course I'm going to say that. She'd be amazing.

"I don't know if that's ever going to happen. Look, Simon's one of the smartest people I know. I'm sure he he's got some very interesting ideas up his sleeve."

Despite Randy being a judge on rival show 'American Idol', he would have no problem with the brunette beauty joining US 'X Factor'.

He added: "She's her own person. She can of course do whatever she wants and she always will do that.

"Simon's one of my dearest friends in the world."

But Randy - who sits on the 'American Idol' panel alongside Steven Tyler and Jennifer Lopez - admitted he was "sad" to see Paula, Nicole and host Steve Jones axed from 'X Factor'.

He explained: "I have not spoken to Paula. We texted back and forth. I'm sad to hear about what's going on with that show. All of those people are dear friends of mine."