TV Guide has some flashback spoilers for us this time:
Now that Elena will transition, how soon before memories she was compelled to forget come back on The Vampire Diaries? — Maxine
NATALIE: We all love a good flashback and fortunately for Delena fans, in the premiere episode Elena will remember a very important moment from Season 2: when Damon told her he loved her. But unlike past flashbacks we’ve seen, Elena doesn’t realize right away that she’s watching a memory from the past rather than experiencing a moment in the present.