From another article:
Protestants traditionally read the New Testament as meaning Mary gave birth to Jesus as a virgin and then had James, three other sons and at least two daughters with Joseph. In accord with church fathers writing after the New Testament era, the Eastern Orthodox and Roman Catholics teach Mary's "perpetual virginity," which means she and Joseph never had marital relations. The Orthodox think Joseph had James by his first wife, and after she died he married Mary - whose only child was the virgin-born Jesus. Thus, James was Jesus' stepbrother. Catholics commonly hold that James was merely Jesus' close relative, perhaps the son of Joseph's brother Clopas or a cousin on Mary's side. The new inscription, if authentic, would rule out that option.
A view not shared by Luther, Calvin or Zwingli.