Or HaChaim on Genesis 45:1/אור החיים על בראשית מ״ה:א׳

1 ולא יכול יוסף להתאפק, Joseph could no longer contain himself, etc. He could not wait until all those present would leave of their own accord, but he called out loudly that everyone other than the brothers be removed from his presence immediately. The Torah adds the words ולא עמד איש אתו, that no one remained with him, to underline the speed with which his servants left his presence.

2בהתודע יוסף, when Joseph revealed himself. The letter ב before התודע means "on account of" (his revealing himself). In order for the brothers to accept Joseph's claim that he was their brother, the matter of his sale had to be aired. Joseph wanted to spare his brothers the embarassment of becoming known as people who had sold their brother, hence he had to clear everyone out of the room. When the Torah mentions immediately afterwards that Joseph wept loudly when he revealed himself and all of Egypt heard about it, this is a clear indication that Joseph was not concerned that he could be overheard. He was only concerned that his brothers' part in all this should not be overheard.