This was confirmed by Rowling in 2007, but is also a fact close readers could have sussed out. Harry and Voldemort are related distantly through the Peverell family. This is how Harry came to have Ignotus Peverell's invisibility cloak and how Voldemort inherited the Resurrection Stone, which is the second hallow.
Rowling has admitted that she "wrote the Hermione/Ron relationship as a form of wish fulfillment. That's how it was conceived, really, For reasons that have very little to do with literature and for more to do with me clinging to the plot as I first imagined it, Hermione ended up with Ron."
In other words, Rowling isn't convinced that it's quite believable that Hermione and Ron would make a good match, although she has said that they might "be alright with a bit of counseling." Emma Watson has agreed that it is questionable as to whether Ron could really make Hermione happy.
One of Rowling's most famous and well received post-Deathly Hallows confessions is that Professor Dumbledore is gay. She shared this information in 2007 during a reading of her final novel in Carnegie Hall, where she explained that Dumbledore was in love with the dark wizard Grindelwald.
In 2007, Rowling shared with the world that Neville's parents, Frank and Alice Longbottom, never recovered from being tortured by Bellatrix Lestrange. Instead, they remain in St. Mungo's Hospital for Magical Maladies and Injuries for the rest of their lives. She commented saying, "I know people really wanted some hope for that, and I can quite see why because, in a way, what happens to Neville's parents is even worse than what happened to Harry's parents. The damage that is done, in some cases with very dark magic, is done permanently."
Even though his parents never recover, Neville blossoms with old age. His grandmother admits that he's talented at wizardry and he gets married to Hannah Abbot. Together, they live above The Leaky Cauldron and Neville spends the rest of his days teaching Herbology at Hogwarts.
Rowling has written that Dolores Umbridge was based off of a person "whom I disliked intensely on sight. The woman in question returned my antipathy with interest. Why we took against each other so instantly, heartily and (on my side, at least) irrationally, I honestly cannot say."
Rowling shared with Daniel Radcliffe that while she had made a promise to herself that Harry, Ron and Hermione would make it out alive, she did come close to killing off Ron. She shared that at the time when she began considering it, she "wasn't in a very happy place" and "I started thinking I might polish one of them off. Out of sheer spite...But I think in my absolute heart of heart of hearts, although I did seriously consider killing Ron, [I wouldn't have done it]."
Ron wasn't the only Weasley that Rowling thought about killing. Arthur almost didn't survive Voldemort's attack by a snake. She knew that she would have to kill at least one Weasley off, because it would have ben unrealistic had every Weasley survived. Arthur ended up making it through until the end because "there were very few good fathers in the book. In fact, you could make a very good case for Arthur Weasley being the only good father in the whole series."
Had Arthur been killed off, Lupin and Tonks may have made it. Rowling knew she "wanted to kill parents" at the end of the story to as "an echo of what happened to Harry, just to show the absolute evil of what Voldemort's doing." She added that, "As happened in the first war when Harry's left behind, I wanted us to see another child left behind. And it made it very poignant that it was their newborn son."
Harry and Dudley don't end up cutting each other from their lives. The two manage to get over their pasts enough to "still see each other enough to be on Christmas card terms, but they would visit more out of a sense of duty and sit in silence so that their children could see their cousins."
Harry and Ron never felt the need to return back to Hogwarts after Voldemort's death. Hermione (obviously) did choose to return and finish by taking her NEWTs.
Ron and Harry (obviously) wound up as Aurors. Given that they'd had a lot of practice, that last year of Hogwarts wasn't too necessary.
Harry, Ron and Hermione all wound up with their own chocolate frog cards, which Ron reported as his "finest hour."
Harry's card says that he is "the first and only known wizard to survive the Killing Curse, most famous for the defeat of the most dangerous dark wizard of all time, Lord Voldemort."
Ron's card gives him credit for "destroying the Horcruxes and subsequent defeat of Voldemort and revolutionizing the Ministry of Magic."
On hers, Hermione gets credit for being "the brightest witch of her age" and that she "eradicated pro-pureblood laws" and campaigned for "the rights of non human beings such as house-elves."
In a particularly hilarious revelation from J.K. Rowling, it turns out sometimes Dumbledore could tell when Harry was snooping. Rowling shared that Dumbledore would silently use the incantation "homenum revelio" to get a glimpse of Harry as he eavesdropped.
It technically doesn't really matter cause he's not to be named, but it turns out that we've been saying Voldemort wrong for the past 18 years. Rowling revealed on Twitter that the 't' in Voldemort was always intended to be silent.
Snape would never have been recognized well at Hogwarts for his stint as Headmaster if Harry had not made sure he was. Rowling has said that she likes to believe that Harry would have made sure Snape's portrait was hung rightfully in the Headmaster's office.
Sirius Black's motorbike got seriously beaten up by some Death Eaters the night Harry left Privet Drive. However, good old Mr. Weasley was able to fix it up and get Harry a dope new ride.
In response to questions from curious fans, J.K. Rowling revealed on August 21, 2015 that "Hagrid couldn't produce a Patronus," with the reason being that "It's a very difficult spell."
In "Deathly Hallows," Hermione has an ever-expanding handbag, which apparently is completely illegal. Despite the Ministry of Magic regulating the spell, she ended up getting away with breaking the law because the bag "played no insignificant part in the defeat of the greatest Dark wizard of all time."
Exciting news, American fans! An American School of Wtchcraft and Wizardry exists! Rowling tempted fans and caused speculation by saying more information would be "revealed in due time" about the school. However, she did share that it is not in New York, that it has a name of "immigrant origin and that historically it would be closely related to Native American culture because of the "indigenous magic" that "was important to the founding of the school."