Question: Who is the mother-in-law of Piers Gaveston, 1St Earl Of Cornwall?
Sentence (from "Margaret de Clare"): Margaret de Clare, Countess of Gloucester, Countess of Cornwall (12 October 1293 – 9 April 1342) was an English noblewoman, heiress, and the second-eldest of the three daughters of Gilbert de Clare, 6th Earl of Hertford and his wife Joan of Acre, making her a granddaughter of King Edward I of England.
Relevant evidence: Yes