St. Joseph was a father to Jesus (Luke 2:48: "… Behold thy father (πατήρ) and I have sought thee sorrowing."), having all the rights a father has over his son, but he was not the natural father of Jesus; all Jesus's flesh came from the blood of His mother, Mary. Nor was he a "foster father", as he didn't adopt his Son from another marriage; Jesus came from within Sts. Mary's and Joseph's true marriage.
Thus, what best describes the sort of father St. Joseph was?