Quando o professor Quirrell começou a compartilhar seu corpo com Voldemort?

Quirrell deixa bem claro que foi depois da invasão fracassada no Gringotes.

“He does not forgive mistakes easily. When I failed to steal the stone from Gringotts, he was most displeased. He punished me… decided he would have to keep a closer watch on me.…”

Quirrell’s voice trailed away. Harry was remembering his trip to Diagon Alley — how could he have been so stupid? He’d seen Quirrell there that very day, shaken hands with him in the Leaky Cauldron.

Harry poderia apertar a mão dele, não querendo dizer Voldemort. Mais tarde, sua cicatriz machuca pela primeira vez quando ele olha para Quirrell no banquete de abertura. Ergo, foi algum tempo no ínterim.

Ele começou depois que o professor Quirrel não conseguiu roubar a Pedra Filosofal do cofre de Gringotes. Do capítulo 17 de Harry Potter e a Pedra Filosofal :

‘I met him [Voldemort] when I travelled around the world. A foolish young man I was then, full of riddiculous ideas about good and evil. Lord Voldemort showed me how wrong I was. There is no good and evil, there is only power, and those too weak to seek it … Since then, I have served him faithfully, […] When I failed to steal the Stone from Gringotts, he was most displeased. He punished me … decided he would have to keep a closer watch on me …’

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