Question: When did Princess Helena Adelaide Of Schleswig-Holstein-Sonderburg-Glücksburg's mother die?
Sentence (from "Count Oluf of Rosenborg"): ( Oluf Christian Carl Axel; 10 March 1923 – 19 December 1990), a former Danish prince, was the younger child and son of Prince Harald of Denmark by his wife, Princess Helena Adelaide of Schleswig- Holstein- Sonderburg- Glücksburg.
Relevant evidence: No