Question: The Oster Conspiracy hoped to reinstate the grandson of which British Monarch as Emperor? 

Context paragraphs:
Emperor of India: The title Emperor/Empress of India was used by the British monarchs during the British Raj in the Indian subcontinent from 1876 (see Royal Titles Act 1876) until 1948, after India had attained independence from the United Kingdom, when for a transitional period the British monarch was also king of the independent dominions of India and Pakistan.

Wilhelm II, German Emperor: Wilhelm II or William II (German: "Friedrich Wilhelm Viktor Albert von Preußen", English: Frederick William Victor Albert of Prussia; 27 January 18594 June 1941) was the last German Emperor ("Kaiser") and King of Prussia, ruling the German Empire and the Kingdom of Prussia from 15 June 1888 to 9 November 1918.  He was the eldest grandchild of the British Queen Victoria and related to many monarchs and princes of Europe.

Governor of the Virgin Islands: The Governor of the Virgin Islands is the representative of the British monarch in the United Kingdom's overseas territory of the British Virgin Islands.  The Governor is appointed by the monarch on the advice of the British government.  The role of the Governor is to act as the "de facto" head of state, and he or she is responsible for appointing the Chief Minister and the Executive Council.

Crown Estate: The Crown Estate is a collection of lands and holdings in the United Kingdom belonging to the British monarch as a corporation sole, making it the "Sovereign's public estate", which is neither government property nor part of the monarch's private estate.  As a result of this arrangement, the sovereign is not involved with the management or administration of the estate, exercising only very limited control of its affairs.  Instead, the estate's extensive portfolio is overseen by a semi-independent, incorporated public body headed by the Crown Estate Commissioners, who exercise "the powers of ownership" of the estate, although they are not "owners in their own right".  The revenues from these hereditary possessions have been placed by the monarch at the disposition of Her Majesty's Government and thus proceed directly to Her Majesty's Treasury for the benefit of the British nation.  The Crown Estate is formally accountable to the Parliament of the United Kingdom, where it is legally mandated to make an annual report to the sovereign, a copy of which is forwarded to the House of Commons.

Oster Conspiracy: The Oster Conspiracy of 1938 was a proposed plan to overthrow German "Führer" Adolf Hitler and the Nazi regime if Germany went to war with Czechoslovakia over the Sudetenland.  It was led by Generalmajor (major general) Hans Oster, deputy head of the "Abwehr" and other high-ranking conservatives within the Wehrmacht who opposed the regime for its behaviour that was threatening to bring Germany into a war that they believed it was not ready to fight.  They planned to overthrow Hitler and the Nazi regime through a planned storming of the Reich Chancellery by forces loyal to the plot to take control of the government, who would either arrest or assassinate Hitler, and restore the exiled Wilhelm II as Emperor.

Black spider memos: The "black spider" memos are letters and memos written by Charles, Prince of Wales, to British government ministers and politicians over the years.  As the modern British monarch remains politically neutral by tradition, the letters are controversial because of Prince of Wales' position as the eldest child of the British monarch Queen Elizabeth II and heir apparent to the British throne.

Chief governor of Ireland: The chief governor was the senior official in the Dublin Castle administration, which maintained English and British rule in Ireland from the 1170s to 1922.  The chief governor was the viceroy of the English monarch (and later the British monarch) and presided over the Privy Council of Ireland.  In some periods he was in effective charge of the administration, subject only to the monarch in England; in others he was a figurehead and power was wielded by others.

Tarquinian conspiracy: The Tarquinian conspiracy was a conspiracy amongst a number of senators and leading men of ancient Rome in 509 BC to reinstate the monarchy, and to put Lucius Tarquinius Superbus back on the throne.  The conspirators were discovered and executed.  The story is part of Rome's early semi-legendary history.

Royal dukedoms in the United Kingdom: In the British peerage, a royal duke is a duke who is a member of the British Royal Family, entitled to the style of "His Royal Highness".  Royal dukedoms are the highest titles in the British roll of peerage.  They are titles created for legitimate sons and male line grandsons of the British monarch, usually upon reaching their majority or marriage.  The titles can be inherited but cease to be "royal" once they pass beyond the grandsons of a monarch.  As with any peerage, once the title becomes extinct, it may subsequently be recreated by the reigning monarch at any time.

Royal coat of arms of the United Kingdom: The royal coat of arms of the United Kingdom, or the Royal Arms for short, is the official coat of arms of the British monarch, currently Queen Elizabeth II.  These arms are used by the Queen in her official capacity as monarch of the United Kingdom.  Variants of the Royal Arms are used by other members of the British royal family; and by the British government in connection with the administration and government of the country.  In Scotland, there exists a separate version of the Royal Arms, a variant of which is used by the Scotland Office.  The arms in banner form serve as basis for the monarch's official flag, known as the "Royal Standard".

Supporting paragraphs: Oster Conspiracy Wilhelm II, German Emperor
Answer: British Queen Victoria