He called himself "king of Great Britain" after gaining England's throne in 1603--he was already king of Scotland
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in Scotland in 1333, he declared himself rightful heir to the French throne in... [DOC] [TLE] Charles I (r. 1625-1649) | The Royal Family - The British Monarchy [PAR] He became heir to the throne on the death of his brother, Prince Henry, in 1612.