Eurus Holmes is the sister of Sherlock and Mycroft Holmes who was completely unknown until her reveal in "The Lying Detective". It is speculated that she exists and is behind the Moriarty "Did you miss me?
Friend:*Falls down the stairs* *Beginning to cry * It hurt so much!It hurt ! Me:Bitch!*Give her 3 Season of Sherlock,All season Doctor who,All season of Supernatural*Watch this and you will feel what pain feels like.