If the two Manchester clubs weren't already at loggerheads before Sunday's derby, they certainly are now.
What happened in the tunnel after Manchester City's 2-1 victory at Old Trafford was genuinely shocking, with Mikel Arteta reportedly sustaining a cut to the head as representatives of both clubs brawled.
It's being widely suggested that Jose Mourinho had milk thrown at him too - all in all, very unsavoury scenes, the likes of which you wouldn't expect from two professional football teams.
That said, perhaps this can all be put down to the pressure of the title race.
Pep Guardiola's side are now a huge 11 points clear of their rivals. The title is effectively theirs to lose and the way they've been playing, it's hard to see them dropping many points between now and May.
Given their luxurious position at the top of the table, it's little wonder they were raucously celebrating in the dressing room, something to which United, and in particular Mourinho, took exception.
The Red Devils boss became embroiled in a row with City goalkeeper and fellow Portuguese speaker Ederson, insisting he showed more respect.
However, according to the Sun, it wasn't just the stopper he had words with.
What Mourinho shouted at City players
Mourinho allegedly told the entire City dressing room:
“Shut up, you’ve won nothing yet. Show some respect, this is the home of United, not you.”
Strong stuff from Jose. He's quite right, of course, in claiming they haven't won anything yet, but it's fair to say they definitely have one hand on the title.
There have been lots of conflicting stories regarding what started the argument. United have it, per the Guardian, that "the walls were shaking" from the music City were playing, both before and after the game.
The hosts ultimately felt that their opponents were showing a lack of class. Meanwhile, the visitors felt that Mourinho simply kicked off because he was being a bad loser.
It's easy to imagine both of those factors playing a part. The two sides now face an anxious wait to hear whether they will be punished by the FA, though there is no CCTV of the incident and referee Michael Oliver was oblivious to what was unfolding outside the referee's room and did not include it in his report.
Do you think City showed a lack of respect to United? Have your say in the comments.