Joseph and Mary were truly married

While clearly affirming that Jesus was conceived by the power of the Holy Spirit, and that virginity remained intact in the marriage (cf. Mt 1:18-25; Lk 1:26-38), the evangelists refer to Joseph as Mary's husband and to Mary as his wife (cf. Mt 1:16, 18-20, 24; Lk 1:27; 2:5).

And while it is important for the Church to profess the virginal conception of Jesus, it is no less important to uphold Mary's marriage to Joseph, because juridically Joseph's fatherhood depends on it.(...)

The Son of Mary is also Joseph's Son by virtue of the marriage bond that unites them: "By reason of their faithful marriage both of them deserve to be called Christ's parents, not only his mother, but also his father, who was a parent in the same way that he was the mother's spouse: in mind, not in the flesh."(13) In this marriage none of the requisites of marriage were lacking: "In Christ's parents all the goods of marriage were realized-offspring, fidelity, the sacrament: the offspring being the Lord Jesus himself; fidelity, since there was no adultery: the sacrament, since there was no divorce."(14)

John Paul II, Apostolic Letter Redemptoris Custos § 7

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13. St. Augustine, De nuptiis et concupiscentia, I, 11, 12: PL 44, 421; cf. De consensu evangelistarum, II, 1, 2: PL 34, 1071; Contra Faustum, III, 2: PL 42, 214.

14. St. Augustine, De nuptiis et concupiscentia, I, 11, 13: PL 44, 421; cf. Contra Iulianum, V, 12, 46: PL 44, 810.