Question: When did Isabella Of Portugal, Duchess Of Burgundy's mother die?
Sentence (from "Henry, son of Robert I of Burgundy"): The first of these derives from an undated obituary from Besançon, Sainte-Etienne, naming "Sibilla, mater ducus Burgundie" (Sibylla, mother of the Duke of Burgundy), it being reasoned that since she is not called duchess, she must have been married to the sole father of a duke who was not a duke himself, Henry.
Relevant evidence: No