His Grace or Her Grace is an English style used for various high-ranking personages. It was the style used to address Kings of England until Henry VIII and the King or Queen of Scots up to the Act of Union of 1707, which united the Kingdom of Scotland and the Kingdom of England. Today, the style is used when referring to archbishops and non-royal dukes and duchesses in the United Kingdom.
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Examples of usage include His Grace The Duke of Norfolk; His Grace The Lord Archbishop of Canterbury; or "Your Grace" in spoken or written address. As a style of British dukes it is an abbreviation of the full formal style "The Most High, Noble and Potent Prince His Grace". Royal dukes, for example the Duke of York, are addressed with their higher royal style, Royal Highness. The Duchess of Windsor was styled "Your Grace" and not Royal Highness upon marriage to Prince Edward, Duke of Windsor.