Miscellaneous
Concerning Hogwarts:
-Harry Potter is the descendant of Godric Gryffindor and possibly his heir.
Outside Hogwarts — Home, Family, Friends and Enemies:
-Mrs. Figgs is a witch. [Note: As far as I can tell from the interviews with JKR, she is important to the plot. She's probably a witch, but it is not confirmed.]
-We will meet Ron's cousin. [Unlikely, see Phantom Characters.]
-We will see Krum again.
-We will see most (not all) of the magical creatures again (Aragog, Buckbeak, etc.) CONFIRMED
-Dudley's best friend turns out to be a wizard.
-We'll learn of Harry's grandparents!
-Some think Dumbledore is Harry's paternal grandfather (James' father). Some think Arabella Figgs is Harry's grandmother (probably maternal: Lily's mother). [This is too cliche to really happen, but something like this could happen.]
-Argus Filch and Mrs. Figgs are related somehow.
-Petunia Dursley will find out she has magical powers.
Magical Community In General:
-The Order of the Phoenix might be a gang of wizards fighting the dark side (though that possibility cannot ruled out). It might be an order like the Order of Merlin.
-Harry Potter receives the Order of the Phoenix (see above rumor) for fighting Voldemort.
Titles and Book Publishing:
Misc.:
-Something big will be discovered about Harry's past. [Maybe that he is Gryffindor's heir?]
-DUMBLEDORE IS IMMORTAL!!!
-Filch finally achieves to become a real wizard
-Pettigrew will end up saving Harry's life
-Ron will be killed by Pettigrew
-Dumbledore will turn traitor (I'm doubtful this will happen)
-Hagrid will betray Harry and/or Dumbledore (probably accidentally)
JK Rowling Tells: (all below is confirmed)
-Harry's middle name is James
-Dumbledore is a hundred and fifty
-Professor McGonagall is seventy
-Snape's 35 or 36
-Wizards have a much longer life expectancy than Muggles
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Someone will, in later books, have their magical powers revealed to them and they will be able to do magic without the seven years of magical education.
-James was Chaser in Quidditch
-"There is more to the Sorting Hat than what you have read about in the first three books," Rowling says. "Readers will find out what the Sorting Hat becomes as they get into future books."
-What determines who gets a letter for Hogwarts? JK Rowling says, "In Hogwarts there's a magical quill which detects the birth of a magical child, and writes his or her name down in a large parchment book. Every year Professor McGonagall checks the book, and sends owls to the people who are turning eleven."
-Lily Potter's maiden name is Evans
-We will see the real Mad Eye Moody in future books.
-JK hinted that Harry might die in the last book.
-JK says Sirius may or may not be cleared in the future; this is important.
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