Later in his reign (1801) the crowns of Great Britain and Ireland were united and he became King of Great Britain and Ireland.
He never was King of England as that title had ceased to exist in 1707 when the crowns of England and Scotland were formally united.
George III was the English king during the American Revolution. His rule began on October 25, 1760 and ended on January 29, 1820.
George III was king of England at the time of the American revolution
England's king during the American Revolution was King George III.
George the Third
King George the Third
King George III