Who is Amaury de Montfort from The Reckoning and what is their importance?

Amaury is Simon and Nell de Montfort's son. His siblings include Henry, Bran, Guy, and Ellen. A priest, Amaury has been imprisoned for over six years on the orders of King Edward. Note, he's been imprisoned without cause. The Pope works relentlessly to garner Amaury's release, and eventually, the king relents.