Who is Monseigneur Charles, Count of Valois from The Iron King and what is their importance?

Monseigneur Charles, the Count of Valois is King Philip's younger brother, and also named variously the Emperor of Constantine and the Ruler of Jerusalem. His many titles are more honorific boasts than they are any real claim to power, as Valois seems fond of collecting bizarre claims through conquest, marriage or treaty to lands that he has no hope of conquering himself.

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