When Yosef reveals himself to his brothers, he says, "אני יוסף העוד אבי חי," "I am Yosef; is my father still alive" (בראשית מ"ה:ג). On this Posuk, the Toldos Yitzchak, among others, raises a question. Why did Yosef ask if his father was still alive, when the brothers had previously told him throughout their conversations with him that he was in fact still living? He explains that Yosef thought that the brothers may have been afraid that he would kill them upon finding out where they were because they had sold him, and so they always claimed that their father was still alive, although in reality he wasn't. Even the wicked Eisav had not wanted to harm Yaakov during Yitzchak's lifetime so as not to bring sorrow upon his father, as the Posuk indicates (שם כ"ז: מ"א). How much more so would Yosef refrain from harming them while his father was still alive; he thus asked here about Yaakov to be certain.
When he sensed his brothers' fear, he said "גשו נא אלי," "Please come near to me, I am Yosef, whom you soldשם מ"ה:ד'( "). "Do not be afraid," he continues, "Hashem sent me here to save you" (שם פסוק ה'). You are not responsible for my being here; Hashem is, because you sold me here as a slave, while Hashem has made me a ruler here. Rabbeinu Bechaya writes that when he said, "I am Yosef your brother", he was saying to them, "even though you sold me, I am still your brother, and will not rule over you."
Some commentators write that when "afterwards his brothers spoke with him" (שם פסוק ט"ו), they begged him not to tell Yaakov that they had sold him, for they were afraid that Yaakov would curse them. Yaakov apparently did not ever know that the brothers had sold Yosef, even to the day of his death, because if Yaakov had known that they had sold him, he would have undoubtedly requested on his death-bed that Yosef forgive them. Yosef himself did not let Yaakov know that he had been sold so that Yaakov should not curse his brothers, and also because his brothers had declared that they would excommunicate anyone who revealed what had happened. Although Yosef was not present at that declaration, it was pronounced by ten men and he thus had to abide by it. We see from all of this that according to Chazal there was a lot more going on here when Yosef reveals himself to his brothers than originally meets the eye.