Isn’t his brother the famous orchestra conductor Otto Klemperer? Were they really Jewish?
Otto Klemperer was his father.
His mother was soprano Johanna Geisler.
His grandmother, from Hamburg, was a Sephardic Jew. Yes, they were really Jewish.
Otto Klemperer was a first cousin of German diarist Victor Klemperer who wrote in his journals about life in the German Empire, the Third Reich and the German Democratic Republic. Published in 1995 his journals, especially the Reich years, are considered golden by writers and academics.