Prince Ernest Augustus, 3rd Duke of Cumberland and Teviotdale

King George V and Queen Marie of Hanover and their children Ernest Augustus, Frederica and Marie.

The young crown prince with his father in the 1860s in "Linden-Hannover"

Prince Ernest Augustus of Hanover, Duke of Brunswick-Lüneburg, Prince of Great Britain and Ireland, was born at Hanover during the reign of his paternal grandfather, Ernest Augustus, King of Hanover. He became the crown prince of Hanover upon his father's accession as George V in November 1851. William I of Prussia and his minister-president Otto von Bismarck deposed George V and annexed Hanover after George sided with the defeated Austria in the 1866 Austro-Prussian War. During that war, the Crown Prince saw action at the Battle of Langensalza.

After the war, the exiled Hanoverian royal family took up residence in Hietzing, near Vienna, but spent a good deal of time in Paris. George V never abandoned his claim to the Hanoverian throne and maintained the Guelphic Legion at his own expense. The former Crown Prince travelled during this early period of exile, and ultimately accepted a commission in the Imperial and Royal Army of Austria-Hungary.

When King George V died in Paris on 12 June 1878, Prince Ernst August succeeded him as Duke of Cumberland and Teviotdale in the Peerage of Great Britain and Earl of Armagh in the Peerage of Ireland. Queen Victoria created him a Knight of the Garter on 1 August 1878. Emperor Franz Joseph I of Austria appointed him to succeed his father as colonel and proprietor of the Austrian 42nd Regiment of Infantry. The regiment's name was changed to honour him, and he served as its honorary colonel from 1879 to the fall of the Austro-Hungarian Empire, in 1918.

While visiting his second cousin Albert Edward, Prince of Wales (later King Edward VII) at Sandringham in 1875, he met Princess Thyra of Denmark (29 September 1853 – 26 February 1933), the youngest daughter of King Christian IX and a sister of the Princess of Wales (later Queen Alexandra).

On 21/22 December 1878, he and Princess Thyra married at Christiansborg Palace in Copenhagen.

Queen Victoria appointed the Duke of Cumberland a colonel in the British Army in 1876[1] and promoted him to major general in 1886, lieutenant general in 1892 and general in 1898. Although he was a British peer and a prince of Great Britain and Ireland, he continued to consider himself an exiled monarch of a German realm and refused to disclaim his succession rights to Hanover, making his home in Gmunden, Upper Austria.

The Duke of Cumberland was also first in the line of succession to the Duchy of Brunswick after his distant cousin, Duke William. In 1879, when it became apparent that the senior line of the House of Welf would die with William, the Brunswick parliament created a council of regency to take over administration of the duchy upon William's death. This council would appoint a regent if the Duke of Cumberland could not ascend the throne. When William died in 1884, the Duke of Cumberland proclaimed himself Duke of Brunswick. However, since he still claimed to be the legitimate King of Hanover as well, the German Bundesrat declared that he would disturb the peace of the empire if he ascended the ducal throne. Under Prussian pressure, the council of regency ignored his claim and appointed Prince Albert of Prussia as regent.

Negotiations between Ernest Augustus and the German government continued for almost three decades, to no avail. During this time, Regent Albert died and Duke John Albert of Mecklenburg was appointed as regent.

The Duke of Cumberland was partially reconciled with the Hohenzollern dynasty in 1913, when his surviving son, Prince Ernst August, married the only daughter of Kaiser Wilhelm II, the grandson of the Prussian king who had deposed his father. On 24 October 1913, he renounced his succession rights to the Brunswick duchy (which had belonged to the Guelph dynasty since 1235) in favour of his son. The younger Ernst August thus became the reigning Duke of Brunswick on 1 November 1913 and married the Kaiser's daughter. As a mark of regard for his daughter's father-in-law, Kaiser Wilhelm II created the elder Ernst August a Knight of the Order of the Black Eagle.

In 1918, the younger Duke Ernst August abdicated his throne along with the other German princes when all the German dynasties were disestablished by the successor German provisional Government which was established when the Emperor himself abdicated and fled Germany in exile to the Netherlands.

Schloss Cumberland in Gmunden, Austria, built in 1882 as exile seat for Ernest Augustus, Crown Prince of Hanover, 3rd Duke of Cumberland and Teviotdale

The outbreak of World War I created a breach between the British Royal Family and its Hanoverian cousins. On 13 May 1915, King George V of the United Kingdom ordered the removal of the Duke of Cumberland from the Roll of the Order of the Garter. According to the letters patent on 30 November 1917, he lost the status of a British prince and the style of Highness. Under the terms of the Titles Deprivation Act 1917, on 28 March 1919 his name was removed from the roll of Peers of Great Britain and of Ireland by Order of the King in Council for "bearing arms against Great Britain."

Prince Ernst August, the former Crown Prince of Hanover and former Duke of Cumberland, died of a stroke on his estate at Gmunden in November 1923. He is interred, next to his wife and his mother, in a mausoleum which he had built adjacent to Cumberland Castle.

Ernest Augustus with family, photographed by Karl Jagerspacher, 1887

The Duke and Duchess of Cumberland had six children: