Stefan and Caroline have shared a special friendship since Caroline's transition into a vampire. Candance Accola spoils that in the next episode of The Vampire Diaries, "My Brother's Keeper", they will make an important discovery together.
"They're both struggling with trying to support the ones they love in difficult circumstances that they don't necessarily agree with," she says. "So they come together over that and find a friendship that's long overdue."
Source: TV Guide