In a scene early in season 1, Roy Kent tells writer Trent Crimm "you're a colossal prick and you always have been". It's the only time they interact in the entire series until season 3.
In a scene from season 2 where Kent is a pundit asked to give his thoughts on a debuting 17-year old prospect, Kent gets super emotional and basically dismisses the entire pundit job, saying it's bullshit that they have to try to sit there and predict what a kid is going to do and judge them when they're not out there with them.
Now you get to the current season, Kent and Crimm are forced into interacting with each other, and Kent reveals that he's kept a newspaper clipping from when he debuted at 17 and Crimm wrote a scathing piece on how shit his debut game was. So in one moment they explained why Kent hated him and why he got choked up about young players being criticized.