Who do Catholics say the Mary in Matthew 27:56 is?

Roman Catholics believe that Mary the mother of Jesus remained a virgin for her whole life. Mary the mother of Jesus is sometimes seen in the gospels with men referred to as Jesus' brothers, with names including James and Joseph. Then there's this verse: Matthew 27:56 (NIV): > Among them were Mary Magdalene, Mary the mother of James and > Joseph, and the mother of Zebedee’s sons. Who does the Roman Catholic Church say this Mary (mother of James and Joseph) was? Were James and Joseph step-children (and therefore Jesus' step-brothers) or perhaps this is a different Mary altogether?