Question: Who is Isabella Of Castile, Duchess Of York's father-in-law?
Sentence (from "Isabella of Castile, Duchess of York"): She accompanied her elder sister, Constance, to England after Constance's marriage to John of Gaunt, 1st Duke of Lancaster, and married Gaunt's younger brother, Edmund of Langley, 1st Duke of York.
Relevant evidence: Yes