Question: Who is Isolde Beidler's maternal grandfather?
Sentence (from "Isolde Beidler"): Isolde Beidler (born Isolde von Bülow: 10 April 1865 – 7 February 1919) was the third of the five stepchildren and children of the composer Richard Wagner and his wife, who is generally known as Cosima Wagner (though the two of them married only in 1870).
Relevant evidence: Yes