Ernst August and his younger brother Christian, were born in Hildesheim, Lower Saxony, while their half-sister, Alexandra was born in Austria and lives with her mother in Monaco. Ernst August was baptized on 15 October 1983 at Marienburg Castle, his godparents including Felipe VI of Spain and Constantine II of Greece.
Ernst August is distantly in the line of succession to the British throne as a descendant of Queen Victoria. Despite the family's residing in Germany through both World Wars, his paternal grandfather obtained British citizenship for himself and his children in November 1956 under the Sophia Naturalization Act 1705, and their family owned property and conducted business in the post-war United Kingdom. Until his mid-teens, Ernst August and his brother lived at Hurlingham Lodge in London.
He also descends from Germany's last emperor, Wilhelm II, following whose abdication at the end of World War I the Hanovers also lost sovereignty over the Duchy of Brunswick, while retaining much of their continental personal property.