Entertainment Tonight ET Online ETOnline.com

And now the real competition begins!

Britney Spears, Demi Lovato, L.A. Reid and Simon Cowell have a better idea what they're in for this season on The X Factor. Following weeks of talent scouting, the foursome learned who they would be mentoring on Wednesday night.

Video: 'X Factor' Guest Mentors Dish on Competition

Alongside guest mentor Will.I.Am, Spears was paired with the teens while Lovato received the young adults (17-24 years) with close pal Nick Jonas.

The girls were happy about their assignments, taking to Twitter to express their delight.

"I'm so excited! …It's definitely the year of the teens on @TheXFactorUSA! #Winners #BritneysTeens," posted Spears.

"Young Adults = #dreamteam. You guys are awesome!!!," wrote Demi.

As for the boys, Simon Cowell happily took on the groups with his co-mentor Marc Anthony while L.A. Reid, with pop sensation Justin Bieber, not so cheerfully received the over-25s.

Video: Britney's Embarrassing Moment on The X Factor

In the end, six talented 12 to 16-year-olds (Diamond White, Beatrice Miller, James Tanner, Carly Rose Sonenclare, Reed Deming and Arin Ray) were chosen to move on with Britney.

Nick Youngerman, Cece Frey, Willie Jones, Jennel Garcia, Paige Thomas and Jillian Jensen were selected as Demi's young adults.

Sister-C, Dope Crisis, and Emblem3 were picked to move on with Simon in addition to boy band Playback, hip-hop threesome Lyric 145 and girl group Lylas, who were all formed by previous solo acts.

Video: Gene Simmons Causes an 'X Factor' Commotion

And, last but not least, L.A. Reid takes on Jason Brock, Darryl Black, David Correy, Tara Simon, Tate Stevens and Vino Alan.

Sadly, fan favorites Sophie Tweed-Simmons (daughter of Gene Simmons) and the inspirational Freddie Combs were among the casualties in tonight's episode.

Tune in tomorrow night at 8/7c on FOX for part two of judges' houses round!