John Wesley on Matthew 1:25

He knew her not, till after she had brought forth - It cannot be inferred from hence, that he knew her afterward: no more than it can be inferred from that expression, 2Sam 6:23, Michal had no child till the day of her death, that she had children afterward. Nor do the words that follow, the first - born son, alter the case. For there are abundance of places, wherein the term first born is used, though there were no subsequent children. Luke 2:7.