J.K. Rowling has revealed the secret bit of information she once shared with the late Alan Rickman, which informed the actor's performance as Severus Snape in the Harry Potter film franchise.
In 2011, Rickman told HitFix that the Harry Potter author shared "one tiny, little, left of field piece of information" to help him understand the Hogwarts Potions Master. At the time Rowling gave him the information, only three of her Harry Potter novels had been published, and he never revealed what it was she told him.
In response to a fan's question about the matter on Twitter, Rowling revealed that she told Rickman the story behind the word "always."
I told Alan what lies behind the word 'always'. https://t.co/NHTJ5J6kxb— J.K. Rowling (@jk_rowling) January 18, 2016
The "always" Rowling is referencing comes from a scene in Harry Potter and the Deathly Hollows, during a conversation Harry overhears while exploring Snape's memories in the pensieve after his death. The conversation is between Snape and Dumbledore, during which Dumbledore reveals that Harry must die if Voldemort is to be killed. Snape grows angry, which surprises both Dumbledore and Harry. Dumbledore wonders if Snape has grown to care for Harry over his years at Hogwarts. In response, Snape summons his patronus, a doe that symbolizes Lily Potter, Harry's mother who died years ago. Dumbledore asks Snape, "After all this time?" Snape simply replies, "Always."
Harry's trip through Snape's memories also reveals that Snape was a childhood friend of Lily's from even before the two attended Hogwarts. He secretly loved her, but they grew apart when Snape became interested in the Dark Arts. James Potter and his friends bullied Snape during his time at Hogwarts, and he grew to resent how Lily fell for James, later focusing much of that lingering resentment on Harry, who looked very much like his father.
"[It] helped me think that he was more complicated and that the story was not going to be as straight down the line as everybody thought," Rickman said. "If you remember when I did the first film she'd only written three or four books, so nobody knew where it was really going except her. And it was important for her that I know something, but she only gave me a tiny piece of information which helped me think it was a more ambiguous route."