In opening 10 of Fairy Tail at 1:15 we see Mavis and Zeref walking towards each other. When their lines of vision meet, a look of deja vu appears on their faces, indicating that they have meet before. Do they know each other and what is their connection? Did they once love each other? (That's the speculation on my part.)
Please watch the opening of Fairy Tail, Number 10 here first before answering my question so you have a better understanding on what I am asking in my question.
Answers are appreciated.