Demi Lovato
Demi Lovato gets into fight with Simon Cowell on The X Factor 2013Screenshot from Official YouTu

Demi Lovato, who has been in the judging panel of "The X Factor USA" since 2012, has announced that she is quitting the show, citing her busy schedule in 2014, which includes touring for her album "Demi". But the timing of her exit has raised many eyebrows.

The 21-year-old singer announced her decision to leave the show during the final live performance night of the "The X Factor" USA 2013 on Wednesday.

"I started the show being a singer and a musician, and so I'm going to go back to that," BBC News quoted the 21-year-old. "It's been really great but I'm so excited for 2014. I'm going to dedicate it completely and entirely to music, touring and making a new album."

Interestingly, Simon Cowell said that he knew Demi was going to quit.

"I always knew she wasn't coming back because she's touring, so I knew that," Cowell told Hollywood Reporter.  

"To avoid speculation. Because of her tour next year it was unlikely she could do that and X factor," he tweeted. "She and I have had our ups and downs but now consider her a true friend. The door will always be open. And thank you Demi. Simon.x."

The fact that he spoke of speculations even before it started, shows that he anticipated the rumours of a rift between them.

Interestingly, Demi Lovato recently told Hollywood Reporter that she would miss Kelly Rowland and Paulina Rubio but didn't mention Simon. "Being able to sit next to Kelly and Paulina and see them twice a week, and also helping mentor the contestants," she said.

Lovato is set to start her Neon Lights tour to support her album, "Demi" in February, and that was the main reason for quitting "The X Factor," but it's also a known fact that her equation with the boss of the show is not the same anymore.

Simon and Lovato used to pull each other's legs in the past and had even admitted in public that they enjoyed it. But off late, they didn't seem to enjoy the banters that they enjoyed not long ago.

The duo got into ugly arguments a couple of times this season and was even stopped by their co-judges on a few occasions. Simon told Demi to shut up after the latter interrupted while the former was giving feedback to Jeff Gutt's rendition of "Hallelujah" by Jeff Buckley in the semi finals. Demi didn't let it go and replied in the same tone.

VIDEO: Simon tells Demi to shut up

Demi and Simon got into another argument after Restless Road and Jeff Gutt performed "Every Breath You Take" by The Police in the semi-finals. Even before Demi could get to what she actually wanted to say, Simon said, "Shocker", leaving the former upset. The visibly angry "Skyscraper" singer stared at Simon before resting her hand heavily on the table, while the latter looked away to have a sip of water. Demi uttered "oh oh" even as Kelly tried to calm her down with a gentle pat on her back to avoid further altercation. She went on to praise the artists without hitting back at her co-judge.

VIDEO: Simon upsets Demi

The fights between Simon and Demi on the show could be just a publicity stunt and may not be the reason for the latter's exit, but what was apparent during the just concluded season is that they don't seem to enjoy each other's company as much as they did last year.