Jerome, on Matt 12:46

“As he was yet speaking to the multitudes, behold his mother and his brethren stood without, seeking to speak to him.”

“(in loc.) But some suspect the brethren of the Lord to be sons of Joseph by another wife, following the idle fancies of apocryphal writers, who have coined a certain woman called E sea. But we understand by the brethren of the Lord, not the sons of Joseph, but cousins of the Saviour, sons of a sister of Mary, an aunt of Our Lord, who is said to be the mother of James the Less, and Joseph, and Jude, whom in another place of the Gospel we find called the brethren of the Lord. (Mark 6:3) And that cousins are called brethren, appears from every part of Scripture.”

Imported from an open dataset — not yet checked against the printed edition.