to a virgin pledged to be married to a man whose name was Joseph, of the house of David. The virgin's name was Mary.
The house of David ...  Commentators have sometimes troubled themselves over the applications of these words, whether to Joseph or to Mary; but they surely apply to both.  That Mary was also of the house of David, as a comparison with  Luke 1:69 shows, Luke would fully prove by the genealogy which he introduced a little later (Luke 3:23f).