23 The Supreme Shepherds of the Church have considered it their duty to promote by eulogy and exhortation the devotion of the Christian people to the heavenly Mother and Queen. Simply passing over the documents of more recent Pontiffs, it is helpful to recall that as early as the seventh century Our predecessor St. Martin I called Mary "our glorious Lady, ever Virgin." St. Agatho, in the synodal letter sent to the fathers of the Sixth Ecumenical Council called her "Our Lady, truly and in a proper sense the Mother of God." And in the eighth century Gregory II in the letter sent to St. Germanus, the patriarch, and read in the Seventh Ecumenical Council with all the Fathers concurring, called the Mother of God: "The Queen of all, the true Mother of God," and also "the Queen of all Christians."
Source: Ad Caeli Reginam (Vatican.va)