This year, it was Remus Lupin, the werewolf wizard who died fighting the evil Lord Voldemort and his minions.
"Arthur lived, so Lupin had to die," Rowling tweeted, referring to another character, Arthur Weasley, who survived the fight.
"I'm sorry. I didn't enjoy doing it.The only time my editor ever saw me cry was over the fate of Teddy," she wrote, referring to Lupin's infant son with fellow wizard Nymphadora Tonks.
Rowling killed off both in the climactic battle to defeat Voldemort, leaving Teddy orphaned.
Rowling, in Lupin's character sketch on her website Pottermore, called the werewolf wizard one of her favorite characters in all of the Potter stories.
"Lupin's condition of lycanthropy (being a werewolf) was a metaphor for those illnesses that carry a stigma, like HIV and AIDS," she wrote. "All kinds of superstitions seem to surround blood-borne conditions, probably due to taboos surrounding blood itself. The wizarding community is as prone to hysteria and prejudice as the Muggle one, and the character of Lupin gave me a chance to examine those attitudes."
Plenty of fans would seem to agree with Rowling's love for Lupin, who was played in the movies by actor David Thewlis.
But, she told Today
back in 2007, she wanted Lupin and Tonks to die as "an echo of what happened to Harry just to show the absolute evil of what Voldemort's doing."
She was referring of course, to Voldemort's murder of Potter's parents.
Rowling said she'd grown too attached to Weasley to let him die, saying he was perhaps "the only good father in the whole series."
This is the third year Rowling has used the anniversary of the Battle of Hogwarts to mourn the deaths of some of her characters.
In 2014, she said she was "having a moment's silence over my keyboard" for the characters who died in her stories.
In 2015, she apologized to fans for the death Fred Weasley -- Potter pal Ron Weasley's brother.
When asked why she chose Weasley's death, she said
, "Fred was the worst for me, so I started with him."
While Rowling isn't saying the deaths were mistakes -- although many have drawn ire from fans who fell in love with various characters -- she has acknowledged there are things she would have changed in the stories.
In 2014, she revealed that she should have had Hermione Granger marry Potter
instead of Ron Weasley.
"It was a choice I made for very personal reasons, not for reasons of credibility," she told Wonderland magazine.
How would you have rewritten Harry Potter? Let us know in a sentence, please, in the comments.