It is important to know the background of things going on while this story is going on.
Henry, King of England, has stolen the throne of England/Normandy after murdering his brother in a Hunting "accident", while his other brother (and rightful king) was still traveling home. It is a dangerous time, Henry is looking to secure his throne from the wild Crusaders that have returned and threaten to destablize things with their plundered treasure.
He is cunning, ruthless, and ambitious.
France is on a knife's edge, Radoslav has renown after his victory (Darien's) in the Holy Lands, but he is home now. And the men who had ruled in his stead while France was under regency are loathe to give up their autonomy. Blades are sharpening, and (as you will see) There is a massive succession crisis coming.
Darien sits right in the middle of these two kings, with a powerful army. And we already know how cold, calculating, and pragmatic Radoslav is when pushed. He left Darien and the Vanguard to die before in the Holy Lands, he will have zero compunction in doing the same to Atreus FitzDarien if it serves his goals.
Control the son, control Darien.
There is a damn good reason Darien HATES crowns.