Here are the author's tweets:
Loads of confused people are asking what's special about tomorrow. It's the 17th anniversary of the Battle of Hogwarts. Just had a thought- J.K. Rowling (@jk_rowling) May 1, 2015
Today I would just like to say: I'm really sorry about Fred. *Bows head in acceptance of your reasonable ire*- J.K. Rowling (@jk_rowling) May 2, 2015
.@Brieuc26Rankin I thought I might apologise for one death per anniversary. Fred was the worst for me, so I started with him.- J.K. Rowling (@jk_rowling) May 2, 2015
Congratulations to Fred Weasley for being the first apology. It's fitting to start with him, since he was a major casualty of the Battle of Hogwarts. George would probably appreciate Fred being honored first -- and maybe make a little joke about not quite hearing her right, so could she repeat it every day.
Any thoughts on who might be next? That fan asked about Lupin and Tonks, but you could add any number of characters -- Sirius Black, Dumbledore, Snape, etc. We're pulling for you, Severus!