Question: Which American author wrote both The Idylls of the Queen, and the "Frostflower and Thorn" series?
Sentence (from "The Idylls of the Queen"): The Idylls of the Queen: A Tale of Queen Guenevere is a 1982 fantasy mystery novel set in the framework of the King Arthur myths written by American author Phyllis Ann Karr.
Relevant evidence: Yes