Queenship of Mary
Encyclical AD CAELI REGINAM of Pope Pius XII
11. St. Gregory Nazianzen calls Mary "the Mother of the King of the universe," and the "Virgin Mother who brought forth the King of the whole world," while Prudentius asserts that the Mother marvels "that she has brought forth God as man, and even as Supreme King."
12. And this royal dignity of the Blessed Virgin Mary is quite clearly indicated through direct assertion by those who call her "Lady," "Ruler" and "Queen."
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More information on Mary's Queenship from here.