Demi Lovato is quitting 'The X Factor' USA.

The 'Heart Attack' hitmaker, who is set to wrap up her second year on the judging panel, alongside Simon Cowell, Kelly Rowland and Paulina Rubio, after tonight's (18.12.13) grand final, will not be returning to the Fox series next year for its fourth season.

A source told ''She has a great time but she's going to focus on her music next year.''

The 21-year-old singer, who released her fourth studio album, 'Demi,' last May, is set to embark on her Neon Lights Tour in February, and will be supported by Little Mix and Cher Lloyd.

Demi, who recently admitted she couldn't go an hour without using cocaine and used to smuggle the drug through airports before she went to rehab in October 2011, previously revealed she wasn't ready to join the reality series when she signed her contract in 2012 but insisted she had no regrets.

She said: ''I don't think I was ready when I started on 'The X Factor.' In an ideal situation I would have maybe waited a year or more.

''I dived into work really quickly and maybe that wasn't the best idea at the time, but the place I am in today is so much better than I could have ever imagined, so I'm really glad.''