Digital Spy had an exclusive interview with Tara actor Amber Benson who recalled Joss pulling her aside during the filming of the season 5 finale.
She said “He was like, ‘Hey! Guess what? It’s so exciting! We’re going to kill your character!’
“I was like, ‘Oh… oh, yes…. That sounds… awesome… yeah.'”
Although she was told that it would be early in season 6, she stated that it was changed multiple times before they finally settled on episode 19.
Read the whole article over at Digital Spy