Complex sentence: Queen Igraine, of the ancient Welsh Kingdom of Powys, has been visiting the Monastery to pray for a child and has learned that humble brother Derfel is in fact the last survivor of Arthur's warriors, and commissions him to write Arthur's story.
Split into simpler sentences: Queen Igraine, of the ancient Welsh Kingdom of Powys, has come to the Monastery to pray for a child. When she learns that humble brother Derfel is the last survivor of King Arthur's warriors, she commissions him to write Arthur's story.