Were Harry and Hermione siblings? The overall ideas behind the Sibling Theory are: -Lily and James Potter secretly had another child before or at the same time as Harry (thus making Hermione Harry's older sibling or twin sister) -They gave the girl to adoptive parents (the Grangers) -Hermione finds out about her adoption, but refrains from telling Harry.
https://www.quora.com/What-is-the-theory-of-Hermione-being-Harrys-sister
