Mrs. Mac and Mrs. Kelly move in together after Mrs. Mac burns her house down. Yes, we know this picture isn't from that episode, but look at them together.
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It's Always Sunny in Philadelphia Season 6 Episode 6 Quotes

Dennis: Mrs. Mac has a unique and earthy fragrance.
Mrs. Mac: I smell like shit.

Frank: Deandra will take care of me.
Dennis: Dee's not gonna take care of you. You just chased her out of here with a pool cue because she had a little cough.