Khloe Kardashian & Mario Lopez -- Officially Sign On to 'X Factor'

It's official ... Khloe Kardashian and Mario Lopez will be the new co-hosts of "X Factor".

TMZ has confirmed with sources connected to the show.

They broke the story ... Khloe and Mario had been thiiiiiiis close to a deal for months ... but now we've confirmed they've both signed on the dotted line ... it's a done deal.

I'm told the duo's salaries will add millions to the budget on top of an already enormous talent budget with Britney Spears in the lead at $15 mil. K&M are expected to debut on the show in November.