Simon Cowell Tells Demi Lovato to 'Shut Up' on Television; 'Skyscraper' Singer Looks Literally Upset [VIDEOS]

"The X Factor" mentors Simon Cowell and Demi Lovato were known for pulling each other's legs and have gone on record saying that they enjoy it, but things seem to have gone out of hand of late with what was supposed to be "just for fun" spinning into heated arguments, and that too on television for everyone to see.

Simon and Demi got into an ugly argument a couple of times during the semi-finals on Wednesday. Co-judges had to intervene on one of the occasions to avoid a possible altercation between the two.

"Shut up Demi", said Simon while giving feedback to Jeff Gutt's rendition of the song, "Hallelujah" by Jeff Buckley. Demi then hit back in the same tune. The exchange of words happened after the "Skyscraper" singer interrupted when Simon was sharing his opinion on the performance.

VIDEO: Simon tells Demi to shut up

As if that was not enough, the two got into another argument after Restless Road and Jeff Gutt performed "Every Breath You Take" by The Police together. 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 shove and 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

It may be recalled that Wednesday's exchange of words was not the first time the two got into heated argument. While responding to Jeff's performance of "Bohemian Rhapsody" by Queen last month, Simon took on Demi by saying, "I'm asking him (Jeff)" a couple of times after the latter interrupted. Kelly and Paulina had to intervene to doze off a possible dirty fight on television.

Simon had also uttered the two-word sentence to Paulina after Jeff's rendition of Mariah Carey's hit song "Without You" earlier this month. The reality television show mogul said, "Pauli just shut up", and then she shot back, "Simon, stop drinking". The exchange of words, which seemed to be in good humor, happened after Paulina interrupted when Kelly was giving her feedback on Jeff's performance. He told her again to shut up after Ellona Santiago's rendition of Lady Gaga's "Applause".

VIDEO: When Simon tells Paulina to shut up

"The X Factor" USA 2013 has reached the penultimate stage with the top four finalists having performed live in the semi-finals on Wednesday. Three of the remaining four contenders - Alex & Sierra, Carlito Olivero, Jeff Gutt and Restless Road - will go to the finals next week while one that gets America's least votes will be sent home on Thursday's episode.