Ernest Augustus ; 17 November 1887 – 30 January 1953) was Duke of Brunswick from 2 November 1913 to 8 November 1918. He was a grandson of George V of Hanover, thus a Prince of Hanover and a Prince of the United Kingdom. He was also a maternal grandson of Christian IX of Denmark and the son-in-law of German Emperor Wilhelm II. The Prussians had deposed King George from the Hanoverian throne in 1866, but his marriage ended the decades-long feud between the Prussians and the Hanoverians.

The Duchy of Brunswick was a historical German state. Its capital was the city of Brunswick . It was established as the successor state of the Principality of Brunswick-Wolfenbüttel by the Congress of Vienna in 1815. In the course of the 19th-century history of Germany, the duchy was part of the German Confederation, the North German Confederation and from 1871 the German Empire. It was disestablished after the end of World War I, its territory incorporated into the Weimar Republic as the Free State of Brunswick.