1. Albus Dumbledore has a ridiculously long name
He's Albus Percival Wulfric Brian Dumbledore. Oh, and by the way, Albus means "white" and Dumbledore is Old English for bumblebee. So he's technically called "White Bumblebee".
2. Hogwarts is close to Aviemore in Scotland
But don't go looking for it; all you'll see is a dilapidated building. The Muggle-repelling charms make sure of that.
3. Hermione is nearly a year older than Harry
Her birthday is September 1979, and Harry's is July 31st 1980. So if Hermione often seems considerably more grown up than her friends… that's because she actually is! (Ron's birthday is March, by the way.) And talking of Harry's birthday.
4. Harry Potter's birthday is the same as JK Rowling's
She chose it deliberately to match hers (though they were born in different years, obviously). What's more, the fact that it's 31st July means that they're both Leos – and the Gryffindor House symbol is a lion. Coincidence?
5. Merlin went to Hogwarts
Yes, you read correctly. Merlin, wizard of the Court of King Arthur (and creator of the Order of Merlin awards), was in fact a Hogwarts alumnus. Oh, and just in case this may change your opinion of him… he was a Slytherin.
6. Dean Thomas's father was a secret wizard
Even Dean, one of Harry's dorm mates in Gryffindor, doesn't know this! His father left him and his mother when he was a baby to protect them from Death Eaters. He never told his wife he was a wizard, but after Dean got his Hogwarts letter, she began to suspect. However, she never shared it with Dean.
7. Malfoy translates to "bad faith"
Did you really think the Malfoys were going to be a family of good eggs, with a surname which literally translates as "bad faith" in French?
8. McGonagall was nearly a Ravenclaw
The Sorting Hat took more than five minutes (a "hatstall") before deciding to sort her into Gryffindor. Can you seriously imagine Gryffindor without Professor McGonagall as Head of House?
9. Voldemort's boggart would have been his own death
Voldemort feared death more than anything, so as JK Rowling confirmed, if he confronted a boggart – which, as we all know, take the form of our worst fears – he would see himself, dead.
10. Harry Potter and Voldemort are actually related
Harry is a descendent of Ignotus Peverell, while Voldemort is descended from his brother Cadmus Peverell. The Peverells were the original owners of the Deathly Hallows – which is how Harry inherited the invisibility cloak.