Their king’s crown - The word rendered “their king” (Malcham) is also the name of the national idol of the Ammonites ([Reference Jeremiah 49…

Their king’s crown. —The same Hebrew letters, translated their king, form the name of Milcom, the chief idol of …

And he took their king's crown from off his head
The crown of Hanun the king of the Ammonites, who now fell into his…

To be this severe in putting the children of Ammon to slavery was a sign that David's heart was not yet softened by repentance, when this took plac…