BELOW CONTAINS MANGA SPOILERS!
After reading the most recent manga update I was shocked when I saw Zeref thanking Layla (also who's Anna?). I started wondering how he knows her. Here are a few possibilities I thought of if you have others please let me know in the comments.
He literally just met her: With how long he lived I know this is probably a likely possibility, however I don't see Hiro doing that, with shocking us that they knew each other I'm guessing there is a clever backstory.
Marvis knew her: He met her through Marvis, again I don't think this would be a clever enough back story but maybe.
They're related: Well while it be a huge plot twist, I don't see it happening due to there being a lot of anger and heart broken shippers. I do think it be interesting though.
The Heartfilia's are a lot more powerful then we realize: We seen Lucy power grow so much throughout the series maybe they have much more power then we even realize and that's why their families came in contact.
I'm sure there are thousands of possibilies, and while we only need to wait until next week to find out. I still would love to know now, so what are you're thoughts.