He's always been that way -- (Patreon)

Some doodles of a young Uncle and how he acted with Julien around.

I went into a lot of depth in the server explaining everything but I pretty much explain Uncle's attachment to Julien as all he really has. His mother died when he was a preteen, his father was much older and died shortly after Julienne gave birth, after which she and her husband just up and abandon the kid, Uncle is fairly young, either early to mid 20's when he's crowned king.

His whole family is gone and he's left to raise a baby, literally all the family he has left and he'll be damned if he doesn't at least TRY for this kid.

I also headcanon the Uncle and Hector were interested in each other, it's more one sided on Hector's part tho. At this time Hector is royal adviser and  Uncle has minimal experience with true romance in any sense, they may have fooled around a time or two but Uncle never sees anything past that and as Julien gets older his attention is for his nephew only.

This results in Hector becoming bitter with time and eventually quitting his job, there never is any resolve for him but he still misses what he used to have when they were younger.