<Tr> <Td_colspan="8"> A vampire named Trevor takes Elena to an abandoned house, where she meets Rose, another vampire . When Tyler witnesses Caroline's abilities, she reveals that she is a vampire . Elena overhears Rose and Trevor arguing about a vampire named Elijah . Using a spell, Bonnie locates Elena . Elena tries to extract information from Rose, who tells her that Elijah is one of the "original" vampires . Rose and Trevor are using Elena, the Petrova doppelgänger who is the key to breaking the curse, as a bargaining chip . Elijah arrives, and Rose offers him Elena in exchange for their pardon . Elijah agrees but kills Trevor . Elena tries to stall Elijah by saying that she knows where the moonstone is, but he compels her to tell him its location . Stefan and Damon arrive to fight with Elijah and stake him . Elena's vervain necklace remains at the house . Later that night, Damon is in Elena's bedroom with her vervain necklace in his hand . He tells her that he loves her but doesn't deserve her, and that Stefan does . Then he compels her to forget what he said . In the abandoned house, Elijah pulls the wooden stake out of his chest . </Td> </Tr> <Tr> <Th> 31 </Th> <Td> 9 </Td> <Td> "Katerina" </Td> <Td> J. Miller Tobin </Td> <Td> Andrew Chambliss </Td> <Td> November 11, 2010 (2010 - 11 - 11) </Td> <Td> 2J5259 </Td> <Td> 3.50 </Td> </Tr> <Tr> <Td_colspan="8"> <Table> <Tr> <Td> </Td> <Td> This episode's plot summary may be too long or excessively detailed . Please help improve it by removing unnecessary details and making it more concise . (November 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table> The episode begins in Bulgaria in 1490 and shows Katherine giving birth to a baby girl . Her father says that she has shamed their family and takes the baby away . In the present, Elena goes to the tomb, where she offers Katherine blood in exchange for the truth - that a doppelgänger from the Petrova line can be used to break the curse . As Katherine's descendant, Elena is the current Petrova doppelgänger . Katherine reveals that she was expelled from Bulgaria and fled to England, where Elijah and Trevor found her . They recognized her as the Petrova doppelgänger and Elijah tried to kill her, but Trevor helped her to escape . She became a vampire so that she could not be used to break the curse . Katherine came to Mystic Falls to offer Klaus what he needed to lift the curse: the current doppelgänger, a witch, a werewolf, a vampire, and the moonstone . She hoped that Klaus would spare her life in exchange for this . Bonnie meets a warlock named Luka and his father . Jeremy is jealous of Bonnie's attraction to Luka . Damon and Rose seek information about Klaus from Rose's vampire friend, Slater, but a healed Elijah overhears them . Damon and Rose sleep together, and Elijah compels Slater to stake himself . It is revealed that Luka and his father are working for Elijah . </Td> </Tr> <Table> <Tr> <Td> </Td> <Td> This episode's plot summary may be too long or excessively detailed . Please help improve it by removing unnecessary details and making it more concise . (November 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table>

When was katherine pierce turned into a vampire
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