39 Certainly, in the full and strict meaning of the term, only Jesus Christ, the God-Man, is King; but Mary, too, as Mother of the divine Christ, as His associate in the redemption, in his struggle with His enemies and His final victory over them, has a share, though in a limited and analogous way, in His royal dignity. For from her union with Christ she attains a radiant eminence transcending that of any other creature; from her union with Christ she receives the royal right to dispose of the treasures of the Divine Redeemer's Kingdom; from her union with Christ finally is derived the inexhaustible efficacy of her maternal intercession before the Son and His Father.
Source: Ad Caeli Reginam (Vatican.va)