Commentary for Genesis 42:8

'ויכר יוסף וגו AND JOSEPH RECOGNISED HIS BRETHREN etc. — because, when he left them they were full-bearded (Yevamot 88a).

BUT THEY DID NOT RECOGNIZE HIM. I.e., at all. And so he no longer needed to make himself appear strange to them. Now in this matter of recognition, our Rabbis have said¹²⁷Kethuboth 27b. that Joseph recognized his brothers because he had left them bearded, but they did not recognize him because when he left them he had no beard and now they found him with a beard.
Now Issachar and Zebulun were but a little older than Joseph,¹²⁸Thus they were also beardless when Joseph left, so how did he recognize them now that they were bearded? but having recognized the older ones, he recognized them all. Moreover, he recognized them because he knew they were bound to come, but they did not recognize him because it did not occur to them that a slave sold to the Ishmaelites should be the ruler of a land.
Rabbi Abraham ibn Ezra says: And he recognized them.¹²⁹Verse 7 here. That is, at first he recognized them to be his brothers, and following that, he looked at each one and recognized him individually.¹³⁰This explains the repetition in Verse 8, And Joseph recognized his brethren, since it refers to individual recognition.

והם לא הכירוהו. Joseph had grown a beard, something, which at 17, when they had last seen him, he had not yet had. Furthermore, the Royal garments were something they would not have associated with their brother. They did not recognise his voice either, as they had never heard him speak Egyptian. Joseph made sure that there was always an interpreter between him and his brothers as we know from verse 23.