5 And now, that We may bring the Year of Mary to a happy and beneficial conclusion, and in response to petitions which have come to Us from all over the world, We have decided to institute the liturgical feast of the Blessed Virgin Mary, Queen. This will afford a climax, as it were, to the manifold demonstrations of Our devotion to Mary, which the Christian people have supported with such enthusiasm.
Source: Ad Caeli Reginam (Vatican.va)