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וידבר יוסף אל בית פרעה, he used intermediaries as a mourner in garments of mourning is not allowed to appear so before the King

אל בית פרעה לאמור, to the household of Pharaoh to tell him, etc. This means that Joseph wanted the members of Pharaoh's household to tell the king not only the facts, but also the manner in which Joseph had related these facts. Joseph had pleaded with Pharaoh's advisers hoping that they in turn would assist him to have his wish approved. Alternatively, the Torah merely mentions the fact that Joseph asked the members of Pharaoh's household to speak to him because we learned in Yuma 4 that unless one gives express permission to relate something one has been told (even if not in confidence), it is forbidden to do so. We know this from when G'd Himself gave permission to relate what He had said (Leviticus 1,1).

דברו נא באזני פרעה, “please tell Pharaoh the following:” the reason why Joseph did not tell this to Pharaoh personally, was that it was forbidden to appear in the King’s palace dressed in mourner’s garb.