Duchess Altburg of Oldenburg (1938-2025) (1938–2025) Parents Princess Helene of Waldeck and Pyrmont Nikolaus, Hereditary Grand Duke of Oldenburg Children Ferdinand Hartmann Freiherr von Erffa Mattias Hartmann Freiherr von Erffa Rudolf Hartmann Freiherr von Erffa Stephan Hartmann Freiherr von Erffa Hurbertus Hartmann Freiherr von Erffa Siblings Duchess Eilika of Oldenburg Duke Peter of Oldenburg Anton-Günther, Duke of Oldenburg Duke Egilmar of Oldenburg Huno Herzog von Oldenburg Duke Friedrich August of Oldenburg Duchess Rixa of Oldenburg Duke Johann of Oldenburg Partners Rüdiger Freiherr von Erffa