The 28-year-old 'Keeping Up With The Kardashians' star - who was rumoured to be in negotiations for several weeks to replace Steve Jones and host the second series of live shows alongside the 'Extra' presenter - has finally confirmed the news and admitted she is nervous ahead of her debut.
Writing on her official website, she said: ''I'm sure you've been hearing the rumours and I'm SO excited that I can finally confirm the news -- I am joining 'The X Factor' as co-host with Mario Lopez.
''I'm a huge fan of the show so I literally fell over in my chair when I heard that I was being considered for the role. The show already has such an incredible panel of judges and it is truly an honour to have been given this opportunity to work with them.
''I'm thrilled, overjoyed and of course a little nervous about this new step in my career, and I can't wait to get started. Wish me luck.''
Former 'Saved By The Bell' star Mario (39) also tweeted: ''Alright guys, it's official... I'll be hosting @TheXFactorUSA! Looking forward to working with @SimonCowell and the rest of the amazing team.''
Pre-taped auditions for the current series of the reality TV show have been airing for several weeks on FOX putting Simon Cowell under pressure to find presenters ahead of the first live show next month.
Simon - who is on the judging panel alongside Britney Spears, Demi Lovato and La Reid - previously admitted he would love to see Khloe host the series but said he was eager to get two presenters this time round after Steve Jones' disappointing solo effort last year.
Following the official announcement, Simon said he is thrilled to have the two popular TV personalities on board.
He said: ''The worst kept secret in Hollywood is out. Mario and Khloe are our hosts. They will debut on our first live show in November and I couldn't be happier.''