Speaking to The Sun, Matt revealed how he spoke winner-to-winner to James.
He said: "I said, 'Look, James, you're very talented but you haven't sold two million records yet, which I have."
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Straight out with the numbers, this man means BUSINESS!
He added: "'You haven't had two top ten albums yet, which I've had. Don't start mouthing off before you've even really left the show.'"
So what was it that got Matt so narked?
Well, the singer was speaking in response to comments James made earlier this week, saying that Matt had never released any 'decent' material.
Something that Matt is understandably not best pleased about.
"I doubt he's even listened to my albums. It's a shame and I hope it doesn't do him too much damage."
While on the subject, we might as well have a quick swoon! Copyright: [LOOK]
"Not only has he offended me but he's offended every other person that's won the X Factor and everyone who works or has written on these albums."
We're surprised he didn't quickly add that he's not angry, he's disappointed.
"That's some of the best songwriters in the world - all these people - and he's now rubbished their work. So it's a pretty s*** thing for him to have said."
However, James has just become the fastest selling X Factor winner of all time and is on track for a Christmas number one.
So the question is just who do you think will have the last laugh?