User blog comment:IamJakuhoRaikoben/Chapter 449: Mavis & Zeref, Review./@comment-756329-20150824165310/@comment-7418318-20150824172107

There are more than 50 years between that event and Layla's birth. Grand-daughter maybe, but I seriously doubt Layla's their direct child.

Not that I'm at all on board for that theory, just stating the odds.