Reincarnated Villain AU; however make it Egg be 'broken into' the proper pack dynamics of his family.
Dunk is a sweetheart and a wonderful muña- but he is most certainly not a dragonshifter like the Targaryens are. Which means he lacks most of the instincts and dynamics young hatchlings like Egg are usually subjected to, instead raising him like a normal human child.
Dragonshifters are beings of hierarchy. Now don't get me wrong. They're fiercely loyal, possessive, and loving towards their packs. And yet there is a strict pecking order with them that people just do not cross. Mostly for the sake of keeping order, partially to ensure everyone's instincts are properly lived out.
Baelor's the patriarch of his pack. He's the King and makes the decisions. He looks after everyone and makes sure every member of his pack is alright; his orders are absolute in return. He's in charge of disciplining unruly hatchlings when their parents have their hands full and making sure everything runs smoothly. Even his broodmates defer to him who come after him in the hierarchy- their authority is especially strong when it concerns their own offspring. After that it's mostly a question of age amongst the kids.
Usually, this is totally normal for a dragonshifter. They get born into it and raised in it; hierarchy and packs are as normal to them as breathing is. Yet Egg was not, ripped away at a young age and thus needs to learn some things. Especially after it becomes obvious that the little dragon seems to fashion himself some sort of leader on his own, territorial as he is over Dunk.
It's nothing personal, really. Baelor isn't even mad about the challenge! He understands his nephew's unique situation and thinks the way the hatchling is trying to puff his chest at him is incredibly cute on top. Maekar, as his sire, bears equal responsibility to introduce his son to the proper mechanics of their species of course. It's kind of a joint project between the brothers.
They start by forcing Egg to submit by scruffing him. Be that in their dragon or human forms, they just grab him exactly at that special spot around his neck that makes him go ragdolled. They scent the little thing so he may carry the smell of their family like he should have had, though Baelor takes care to ensure whatever weak human scent Dunk is able to leave on the boy remains somewhat. Maekar makes him sleep in a cuddle pile alongside his siblings, both nesting and denning with the boy to slowly get him more comfortable. It's a long process, but it does take effect sooner or later.
Dunk thinks that his squire is bonding with his family in the meantime. Logically, he knows about the dragonshifter stuff from reading the novel- however not only was that like. Multiple years ago by that time but it's also something entirely different to know about something as a reader and clock it when it's in action. Part of him is a little sad watching his boy go like that....ah, well. He supposed the time had to come eventually. Egg is with his real family now, so it's only reasonable he starts being around them more. Dunk should consider himself lucky for the small amount of time he managed to have with him in the first place. He can go and see how it develops then to give Egg enough time to let go of him fully and transition into the dynamics of his family without any issue. After which he could then talk to Baelor about maybe switching posts or leaving for the hedges once more. Dunk doubts he could bear having to witness his boy forget him, even if he knows he will be happier for it...
(Egg won't. Dragon hatchlings don't mess around with their imprints. Everyone knows but Dunk. Part of the reason Baelor is taking such care to 'break' Egg in is that he lowkey wants to court the knight. He doesn't need a hatchling being all territorial and annoying over their muña while doing so. Teaching him who his patriarch is will take care of that issue the quickest way possible)