The Black Dragon by Kathryn Le Veque

Addax al-Kort was not born in England.
As the heir to the throne of a defunct distant kingdom (near present day Pakistan), Addax came to England with a trade caravan when he was very young. He became a page for a powerful knight and worked his way through the ranks and protocols of Medieval England to become a full-fledged English knight serving William Marshal. Addax is part of the brotherhood of Executioner Knights serving the Marshal, but he has a great talent for the tournament circuit. Competing under a standard emblazoned with black dragon, he becomes quite rich.
But something changes the course of his life forever.