Harry: "He made seven Horcruxes?"
Dumbledore: "...Not seven Horcruxes: six. The seventh part of his soul, however maimed, resides inside his regenerated body..." (HP6, US Hardback, page 503).
I would think that Dumbledore had already known that there were 5 horcruxes:
- the diary
- Gaunt's ring
- Salazar's locket
- Helga Hufflepuff's cup
- Nagini (the whole essence divided thing)
Now those are the five that he was sure of. We know that there was also:
- Ravenclaw's diadem
He knew that when Riddle came to Hogwarts to ask for the DADA position, he was really there so he could hide a horcrux. (But he never got a chance to tell Harry that, right?) Did Dumbledore know of the diadem? Or did he just think Riddle wanted to hide the cup?
Did Dumbledore say there were 6 and not 7 because he didn't know about the diadem but did know about Harry being a horcrux? Or did he say there were 6 to ensure Harry didn't guess he was a horcrux? Sorry if this makes no sense.
I know that in the end there were 7 horcruxes and an 8th part of Voldemort's soul right?