The younger Ernest Augustus became heir apparent to the dukedom of Cumberland and to the Hanoverian claim upon the deaths of his two elder brothers, George and Christian.

Through his mother, he was a first cousin of Christian X of Denmark, Haakon VII of Norway, George V of the United Kingdom, Constantine I of Greece and Nicholas II of Russia.

After Prince Albrecht's death in 1906, the duke offered that he and his elder son, Prince George, would renounce their claims to the Duchy of Brunswick in order to allow Ernest Augustus, his only other surviving son, to take possession of the Duchy, but this option was rejected by the Bundesrat and the regency continued, this time under Duke Johann Albrecht of Mecklenburg-Schwerin, who had previously acted as regent for his nephew in Mecklenburg.

When Ernest Augustus's older brother George died in an automobile accident on 20 May 1912, the German Emperor, Wilhelm II, sent a message of condolence to the Duke of Cumberland.

In response to this friendly gesture, the Duke sent his only surviving son, Ernest Augustus, to Berlin to thank the Emperor for his message.

In Berlin, Ernest Augustus met and fell in love with the emperor's only daughter, Princess Victoria Louise of Prussia.

In addition to the German Emperor and Empress and the Duke and Duchess of Cumberland, King George V and Queen Mary of the United Kingdom and Tsar Nicholas II attended.

Upon the announcement of his betrothal to Princess Victoria Louise in February 1913, Ernest Augustus swore allegiance to the German Empire and accepted a commission as a cavalry captain and company commander in the Zieten–Hussars, a Prussian Army regiment in which his grandfather (George V) and great-grandfather (Ernest Augustus) had been colonels.

Ostensibly desiring to pursue an alliance with the UK, in the mid-1930s, Adolf Hitler took advantage of their sentiment by asking the couple to arrange a match between their daughter Princess Frederica and the Prince of Wales.