Or HaChaim on Genesis 45:4/אור החיים על בראשית מ״ה:ד׳

1 ויאמר יוסף אל אחיו גשו נא אלי, Joseph said to his brothers: "please come closer to me." The reason he asked them to come close was so that when he would mention the fact that they had sold him he could whisper. Only after they had come closer did he say: "I am your brother Joseph whom you sold, etc." Joseph was careful to say all this in a whisper although he had sent everybody outside. He was familiar with the proverb that walls have ears.

2אני יוסף אחיכם, "I am your brother Joseph." The reason he repeated the fact that he was Joseph a second time was that he felt there were two reasons why the brothers had not yet responded to him. 1) They were afraid of him and could not answer him just as a thief cannot answer when he is found out suddenly. 2) They simply did not believe him when he claimed to be Joseph. He said: "I am Joseph your brother, does my father still live, etc.?" in order to dispel their fear of him. He stressed the word your brother in that sentence. In the next sentence, after he had formed the impression that they did not believe him, he stressed the words your brother whom you have sold, indicating that even at the time they had sold him he had not ceased feeling like a brother towards them. He added the words "whom you have sold to Egypt" as proof that it was he, Joseph, for not even a prophet could have knowledge of that fact except he himself (compare Yalkut Shimoni 142).