Christian August II, Duke of Schleswig Holstein Sonderburg Augustenburg

Christian August II, Duke of Schleswig-Holstein-Sonderburg-Augustenburg (19 July 1798 – 11 March 1869, Christian Carl Frederik August), usually simply known by just his first name, Christian, Duke of Augustenborg, was a claimant to the rulership of the provinces of Slesvig and Holstein, and the fiefholder of Augustenborg and Sønderborg. He was a prince of the House of Schleswig-Holstein-Sonderburg-Augustenburg and a cadet-line descendant of the Danish royal House of Oldenburg.

He was the eldest son and heir of Princess Louise Auguste of Denmark and Frederik Christian II, Duke of Augustenborg. As such, he was high in the line of succession to the Danish throne. He was the brother-in-law of King Christian VIII and nephew of King Frederick VI.

In 1848, German-nationalist sympathies prompted a rebellion in Schleswig-Holstein against Danish rule. A provisional government was established at Kiel under the Duke of Augustenborg, who travelled to Berlin to secure the assistance of Prussia in asserting his rights. The First War of Schleswig ensued.

However, European powers were united in opposing any dismemberment of Denmark. Among others, Emperor Nicholas I of Russia, speaking with authority as Head of the elder Holstein-Gottorp line, regarded the Duke of Augustenborg a rebel. Russia had guaranteed Schleswig to the Danish crown by the treaties of 1767 and 1773.

A treaty of peace between Prussia and Denmark was signed at Berlin on 2 July 1850. Both parties reserved their antecedent rights. Denmark was satisfied that the treaty empowered the king-duke to restore his authority in Holstein with or without the consent of the German Confederation. Augustenborg was ousted from power, as Danish troops marched in to subdue the duchies.

The question of the Augustenburg succession made an agreement between the major powers impossible, and on March 31, 1852 the duke of Augustenburg resigned his claim in return for a money payment. Duke Christian sold his rights to the Duchy of Schleswig-Holstein to Denmark in aftermath of Treaty of London, but later renounced his rights to the Duchy of Schleswig-Holstein in favor of his son Frederik August.

In 1864, his son Frederick of Augustenborg proclaimed himself rightful Duke of Schleswig and Holstein.

Duke Christian August died 1869.