From 1714 to 1837, the rulers of Great Britain (and later the United Kingdom) were also the rulers of Hanover through a personal union. The same monarch wore both crowns.
The connection began when George I, Elector of Hanover, inherited the British throne after the death of Queen Anne under the rules of the Act of Settlement 1701, which ensured a Protestant succession.
Because the British monarch was simultaneously ruler of Hanover, the British royal coat of arms was modified to include Hanoverian symbols.
The union ended in 1837 when Queen Victoria became queen of Britain. Hanover followed Salic law, which barred women from inheriting the throne, so Hanover passed to her uncle Ernest Augustus instead. After that, the British royal arms dropped the Hanoverian section.
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