After a king dies a mysterious death, the king’s seductive influential adviser calls the impressionable son to the throne to assume control, unaware that he is secretly investigating his father’s death to make sure he isn’t next to risk the fall of the kingdom.

You switch PoV in your logline.
It begins from the adviser point of view, then switches to the young prince's view.
A logline should be told from one point of view, and that is the PoV of the lead character

Which brings us to the next important question...

Who is the lead character? The kid or the adviser.

I like the plot. Suggested format-

"After being enthroned, an impressionable prince must secretly investigate his father?s disappearance to avoid the same"

Isn't the rule passed hierarchically anyways?
What's the advisor's role in it?