Question: What was Johann Ernst Plamann's pupil, the future German chancellor, Duke of?

Context articles: Rut Brandt
John Ernest I, Duke of Saxe-Weimar
Prince Johann Ernst of Saxe-Weimar
Otto von Bismarck
Johann Ernst von Sachsen-Weimar
Johann Ernst III, Duke of Saxe-Weimar
John Ernest, Duke of Saxe-Coburg
Saxe-Saalfeld
Johann Ernst Plamann
Johann Ernst, Count of Hanau-Münzenberg

Rut Brandt (10 January 1920 – 28 July 2006) was a Norwegian-born German writer and the wife of the German Chancellor Willy Brandt between 1948 and 1980, including most of his political career as Governing Mayor of Berlin (1957–1966) and German chancellor (1969–1974).
 Rut Brandt became highly popular in Germany and a noted public figure in her role as First Lady of Berlin and the chancellor's spouse.
Johann Ernst I, Duke of Saxe-Weimar (Altenburg, 21 February 1594 – Sankt Martin, Hungary, 6 December 1626), was a duke of Saxe-Weimar.
Johann Ernst of Saxe-Weimar (German: "Johann Ernst von Sachsen-Weimar" ) (25 December 1696 – 1 August 1715) was a German prince, son by his second marriage of Johann Ernst III, Duke of Saxe-Weimar.
 Despite his early death he is remembered as a collector and commissioner of music and as a composer some of whose concertos were arranged for harpsichord or organ by Johann Sebastian Bach, who was court organist in Weimar at the time.
Otto Eduard Leopold, Prince of Bismarck, Duke of Lauenburg (1 April 1815 – 30 July 1898), known as Otto von Bismarck (] ), was a conservative Prussian statesman who dominated German and European affairs from the 1860s until 1890.
 In the 1860s, he engineered a series of wars that unified the German states, deliberately excluding Austria, into a powerful German Empire under Prussian leadership.
 With that accomplished by 1871, he skillfully used balance of power diplomacy to maintain Germany's position in a Europe which, despite many disputes and war scares, remained at peace.
 For historian Eric Hobsbawm, it was Bismarck who "remained undisputed world champion at the game of multilateral diplomatic chess for almost twenty years after 1871, [and] devoted himself exclusively, and successfully, to maintaining peace between the powers".
 However, his annexation of Alsace-Lorraine gave new fuel to French nationalism and promoted Germanophobia in France.
 This helped set the stage for the First World War.
Johann Ernst von Sachsen-Weimar or Johann Ernst of Saxe-Weimar can refer to:
Johann Ernst III, Duke of Saxe-Weimar (Weimar, 22 June 1664 – Weimar, 10 May 1707), was a duke of Saxe-Weimar.
John Ernest (German: "Johann Ernst" ) (10 May 1521 – 8 February 1553) was a Duke of Saxe-Coburg.
The Duchy of Saxe-Saalfeld was one of the Saxon Duchies held by the Ernestine line of the Wettin Dynasty.
 Established in 1680 for Johann Ernst, seventh son of Ernest I, Duke of Saxe-Gotha.
 It remained under this name until 1699, when Albert, Duke of Saxe-Coburg died without sons.
 His brother Johann Ernst of Saxe-Saalfeld became the new Duke of Coburg and the duchy was renamed into Saxe-Coburg-Saalfeld in 1735.
Johann Ernst Plamann (22 June 1771, Repzin3 September 1834, Berlin) was a German child educator.
 He based his work on the ideas of Johann Heinrich Pestalozzi and Friedrich Ludwig Jahn.
 Among his pupils was future German chancellor Otto von Bismarck.
Johann Ernst of Hanau-Münzenberg-Schwarzenfels (13 June 1613 in Schwarzenfels – 12 January 1642 in Hanau), was the last Count of the Hanau-Münzenberg line.
 He succeeded his grand-nephew Philipp Ludwig III in 1641.
 When Johann Ernst died in 1642, Hanau-Münzenberg fell to the Hanau-Lichtenberg line.