when do they find out katherine is in elena
No Exit (The Vampire Diaries) Damon wakes up chained on the Salvatore house's basement. Stefan is there and Damon tries to warn him that because of his cravings, one day he will kill him but Stefan tells him that they will find a solution. Damon points to Stefan that "Elena" provoked him to feed on her and then she kicked a stake towards him so he will kill him. Stefan does not believe that Elena would want that, he locks Damon up and gets upstairs where Caroline is. The two of them discuss what happened between Stefan and "Elena" and Caroline also tells him about Nadia and Matt and the text he sent to her. From Matt's text, who used "K" and not "E", they put the pieces together and they realize that Katherine is in Elena's body.
Juliet Burke Juliet and Sawyer make their way to the church, where they reunite with other former denizens of the Island. After Christian Shephard opens the doors of the church, she moves on to the next reality while holding hands with Sawyer, her island lover.
Damon Salvatore Damon spends the next two seasons devoted to Elena, waiting for her to wake up. He repeatedly states that he is miserable without her, and will spend the next 60 or so years unhappily until Bonnie dies. However, Damon is committed to staying true to Elena, and doing right by her. Elena is shown to be Damon's moral compass, and his guiding force throughout the two seasons. When Damon is in the Phoenix Stone's version of hell, a vision of Stefan asks Damon "What would Elena do?" and this prompts Damon to forgive his mother, freeing him from hell. The phoenix stone's influence remains, and Damon accidentally lights Elena's coffin on fire (or so he thinks). Believing that he has unwittingly killed the love of his life, Damon becomes suicidal. When confronted with the hunter Rayna, Damon commands her to kill him because he is already in hell in a world without Elena. Enzo then reveals to Damon that Elena is still alive, renewing Damon's hope. When Damon realizes that he is a potential danger to his friends and family because he does not believe he is good without Elena, he decides to desiccate himself next to her. He write to Alaric that before Elena, he didn't know what it was like to be happy, fulfilled or complete, and that he doesn't want to continue living without that feeling. After Stefan wakes Damon from his desiccation, Damon continues to be devoted to his future with Elena. At the end of season 7, he is lured into a trap by a siren, hearing Elena's voice calling out to him. When the siren takes control of Damon's mind in season 8, Damon spends a significant amount of time sleeping, seeking refuge in dreams of his memories of Elena. When Sybil erases Elena from Damon's consciousness only to insert herself into their memories, Damon fights back, instinctively drawn back to Elena. His love for her prevails, and he breaks the siren's mind control, regaining his memories of Elena. Julie Plec stated that "I think the only hope that he's holding on to is the idea of the two of them living in Tribeca in their brownstone and raising kids and having a life together as humans when this is all said and done." [15] After Stefan gives Damon the cure to vampirism, turning him into a human, and Bonnie unbreaks the spell on Elena, Damon and Elena finally reunite. They begin their life together, getting married while Elena goes to medical school and becomes a doctor. Eventually they return to Mystic Falls to grow old together, where they died together of old age. We last see them walking hand in hand in the afterlife before reuniting with their respective families.
Killer Within Outside the prison, an unidentified individual lures a group of walkers towards the prison, breaking open the front gate's lock to allow them inside.