1946 his younger brother Prince George William married Princess Sophie of Greece and Denmark, thus becoming the brother-in-law of Prince Philip, Duke of Edinburgh and Queen Elizabeth II of the United Kingdom. Ernest Augustus was himself an heir to the British titles of Prince of Great Britain and Ireland, recognised ad personam for Ernst August's father as well as for him and his siblings by King George V of the United Kingdom on 17 June 1914, Duke of Cumberland and Teviotdale, Earl of Armagh, which however were all suspended under the Titles Deprivation Act 1917. In addition to being a German, he also held British nationality, after successfully claiming it under the Sophia Naturalization Act 1705 in the case of Attorney-General v. Prince Ernest Augustus of Hanover. Nonetheless, a problem arose as foreign royal titles can't be entered into a British passport. Therefore, the titles Prince of Hanover, Duke of Brunswick and Lüneburg could not be mentioned there, nor could the British titles due to the Titles Deprivation Act of 1917. The name which was finally entered into his British documents, was thus Ernest Augustus Guelph, with the addition of His Royal Highness. Guelph is thus also the British last name of his siblings and children, all styled Royal Highnesses in the United Kingdom. In 1961 he sold his remaining properties at Herrenhausen Gardens, including the site of Herrenhausen Palace which had been destroyed by a British bombing raid in 1943. He kept however the Princely House, a small palace built in 1720 by George I of Great Britain for his daughter Anna Louise. Ernest Augustus converted Marienburg Castle into a museum in 1954, after having moved to nearby Calenberg Demesne, which caused a row with his mother, who was forced to move out. He also sold the family's exile seat, Cumberland Castle at Gmunden, Austria, to the state of Upper Austria in 1979, but his family foundation based in Liechtenstein kept vast forests, a game park, a hunting lodge, The Queen's Villa and other property at Gmunden. The family property is now managed by his grandson Ernst August. Marriage and children During the Second World War, specifically in 1941, his cousin Prince Hubertus of Prussia married the noted society beauty and aristocrat Baroness Maria Anna von Humboldt-Dachroeden (1916–2003). The couple, however, divorced in 1943, after her affair with her husband's cousin, Prince Ernst August of Hanover, resulted in the