His Grace and Her Grace are English styles of address used with high-ranking personages, and was the style for English monarchs until Henry VIII (r. 1509–1547),[1] and for Scottish monarchs until the Act of Union of 1707, which united the Kingdom of Scotland and the Kingdom of England.
The correct style is “Your Grace” in spoken and written form; as a stylistic descriptor for British dukes, it is an abbreviation of the full, formal style: “The Most High, Noble and Potent Prince His Grace”.
The style "His Grace" and "Your Grace" is used in England and some other English-speaking countries to address Catholic archbishops whose seats have come from an English diocesan background, which is not common in other countries (e.g. in France, the Philippines, and the United States Catholic bishops are addressed using the style "Excellency").
In Ireland, the style "His/Your Grace" (Irish: A ghrása) is traditionally used for all Catholic bishops, not just archbishops.
In Islam, several Sufi orders (such as the Qadrianis and Hawariyun) may refer to their spiritual Grand Masters with the honorific "(Most) Gracious ..." or "His Grace" in reference style, while the spoken style is "(Most) Gracious".