Who was the last King of England?

The last person to hold the title "King of England" was King William III.

He reigned jointly with his wife, Queen Mary II from 13th February 1689 and, following the death of Queen Mary on 28th December 1694, reigned alone until his death on 8 March 1702. He held the titles "King of Scotland"(as William II of Scotland) and "King of Ireland" separately.

Under the reign of his successor, Queen Anne, in 1707 the crowns of England and Scotland were united, the title "King (or Queen) of England" ceased to exist and Queen Anne became Queen of The United Kingdom of Great Britain. She was still, separately Queen of Ireland.

In 1801, during the reign of King George III, the crowns of Great Britain and Ireland were united and he became King of The United Kingdom of Great Britain and Ireland.

In 1922 the southern part of Ireland was partitioned and became a separate, sovereign state which is now The Republic of Ireland.

The six Northern counties remained part of the United Kingdom and the the King, George V, became King of The United Kingdom of Great Britain and Northern Ireland.
The last King of The United Kingdom was George VI, and the current monarch is his daughter, Queen Elizabeth II.

She is not, and never has been, The Queen of England.