Duke Johann of Oldenburg (1940-2025) (1940–2025) Parents Duke Nikolaus, Hereditary Grand Duke of Oldenburg Princess Helene of Waldeck and Pyrmont Children Tatiana von Holstein-Gottorp, Herzogin von Oldenburg Constantin Nikolaus von Holstein-Gottorp, Herzog von Oldenburg Eilika Duchess of Oldenburg Siblings Duchess Eilika of Oldenburg Duchess Altburg of Oldenburg Duke Peter of Oldenburg Anton-Günther, Duke of Oldenburg Duchess Rixa of Oldenburg Duke Friedrich August of Oldenburg Duke Egilmar of Oldenburg Huno Herzog von Oldenburg Partners Ilka Gräfin zu Ortenburg