J.K. Rowling, master storyteller that she is, saved some of the best Harry Potter secrets 'til last. We're talking after all of the books were published! What's your favorite late-reveal Harry Potter secret?
1. The connection between Harry and Voldemort goes even deeper...
Fact: Harry Potter and Tom Riddle are actually blood relatives - they're family!
The Explanation: You may have worked this one out yourself - Harry inherits his invisibility cloak from his ancestor Ignotus Peverell, and Tom Riddle inherited the resurrection stone from Cadmus Peverell, Ignotus' brother. Of course, while confirming the blood link between Harry and Voldemort, JK also asserts that 'nearly all wizarding families are related if you trace them back through the centuries.'
2. Holy Harry on a Bike!
Fact: Adult Harry rides Sirius Black's old motorbike
The Explanation: Arthur Weasley - lover of all Muggle paraphernalia - kept the pieces of the bike after it was broken in the Order of the Phoenix vs Death Eaters aerial battle. Arthur mended the bike in his shed and gave it to Harry.
3. Momento Mori
Fact: JK originally planned to kill off Ron and Arthur Weasley instead of Lupin and Tonks
The Explanation: during a spate of personal unhappiness, JK thought about killing off Ron. Once she'd nixed that idea, she turned her mighty pen to Arthur, deciding that it was purely mathematically likely that one of the Weasley bunch would get killed at the Battle of Hogwarts. Obviously, we all know which Weasley ended up taking one for the team.
The reason Rowling rounded on Lupin and Tonks wasn't so much personal to them as what they represented: she needed an orphaned child to bring Harry and Voldemort's orphan narrative full circle. She also revealed that Teddy, with Harry as Godfather, breaks the negative cycle because he is loved deeply by his non-biological family, and grows up happy.
4. LGBT Hogwarts
Fact: Dumbledore is gay
JK confirmed that famed Hogwarts headmaster and all-round wise, awesome dude Albus Dumbledore was always gay, and the great love of his life was none other than Gellert Grindelwald. I hope JK lets on more about their relationship - a true Potter Encyclopedia companion book to the series, please!
5. Wizard School Dropout, Achievement in Confectionery
Fact: Only Hermione ever finished her N.E.W.T.s
The Explanation: When the small matter of The Dark Lord taking over the wizarding world disrupts their seventh year at Hogwarts, Harry, Ron and Hermione leave their studies to fight the good fight. However, JK confirmed that only Hermione actually bothered to go back to sit her exams after Voldemort's downfall. Still, it's not like their lack of paper qualifications kept any of them back: JK said after the novels were released that all three went on to high ranking vital roles in the Ministry of Magic and - perhaps best of all - were immortalized on Chocolate Frog cards, too!
Source: Harry Potter Wiki