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The coronation involves an oath, magically enforced, that she had no hand in the nephew's death; by keeping him alive, she is using Exact Words.
After he squelches a rebellion, King William has the boy they claimed was his grandnephew kept prisoner at his castle, because he was too young to understand what the rebels meant but was too dangerous to let loose.
Subverted: Rumors spread about a prisoner in a tower, but investigating finds that actually, the Necromancer has his younger brother, an alchemist, there, because the brother hates intrusion into his study and work.
Double Subverted: Except that the Necromancer has no brother; he had used magic on the king's mind and body to convince him that they were brothers, and he was an alchemist.
Parodied: The rightful heir to the throne is kept in his suite as much as possible because he's batty. Every now and again he screams for help from the window, but anyone who goes to help him finds he has forgotten it already.
Zig Zagged: The Necromancer may be on the throne, and the King may be imprisoned, but it's unclear which of them is truly in charge.
Averted: The Necromancer kills King William instead of imprisoning him.
Exploited: The Reverse Mole tracks down the king and rescues him.
Defied: The Necromancer kills the king rather than risk a rescue.