In Scene nine, who stops by unexpectedly to see Blanch? Later, what does Blanch tell Stanley was the reason Mitch came to see her?

In Scene Nine, Mitch drops by unexpectedly. Later, Blanche tells Stanley;

BLANCHE: Yes, swine! Swine! And I'm thinking not only of you but of your friend, Mr. Mitchell. He came to see me tonight. He dared to come here in his work-clothes! And to repeat slander to me, vicious stories that he had gotten from you! I gave him his walking papers....

STANLEY: You did, huh?

BLANCHE: But then he came back. He returned with a box of roses to beg my forgiveness! He implored my forgiveness. But some things are not forgivable. Deliberate cruelty is not forgivable. It is the one unforgivable thing in my opinion and it is the one thing of which I have never, never been guilty. And so I told him, I said to him, "Thank you," but it was foolish of me to think that we could ever adapt ourselves to each other. Our ways of life are too different. Our attitudes and our backgrounds are incompatible. We have to be realistic about such things. So farewell, my friend! And let there be no hard feelings....