J.K. Rowling only regrets killing one character in her best-selling Harry Potter novels - and it's no one that you would ever expect. 

Florean Fortescue, the Diagon Alley ice cream parlor owner, was a character so minor he didn't appear in any of the eight movies. Despite his minor role he is the only character Rowling wishes she hadn't killed (She even told US Weekly that she regrets this more than killing major fan favorites including Fred Weasley, Dobby, Sirius Black, and Remus Lupin).

"I seemed to have him kidnapped and killed for no good reason," Rowling wrote on Pottermore. "He is not the first wizard whom Voldemort murdered because he knew too much (or too little), but he is the only one I feel guilty about, because it was all my fault."

Florean was kidnapped from his ice cream shop in 1996 by Death Eaters and later murdered by Voldemort when he refused to tell Voldemort what he knew about the Elder Wand and the lost diadem of Rowena Ravenclaw. 

"I originally planned Florean to be the conduit for clues that I needed to give Harry during his quest for the Hallows, which is why I established an acquaintance fairly early on,"Rowling wrote on Pottermore. "The problem was that when I came to write the key parts of Deathly Hallows, I decided that Phineas Nigellus Black was a much more satisfactory means of conveying clues. Florean's information on the diadem also felt redundant, as I could give the reader everything he or she needed by interviewing the Grey Lady."