That was really surprising (with how Zeref seemed more isolate kind of character and how he was seen throughout the manga before this).
Hiro always seem to pull a rug under me when it comes to these situations (like Zeref not being the evil mage he was intially portrayed, Gajeel turning good, Cana is Gildartz's daughter, Mystogan's identity, Grimoire Heart's master was Fairy Tail's second Master, etc.)
After Zeref's speech to Acnologia from his last chapter, it wouldn't surprise me that Zeref is somehow going to use the entire Albareth kingdom as a means to declare his "annihilation" towards humanity (like destroy the country) or uses it to revive E.N.D. (since "reviving" E.N.D seems to require a continent worth of power like Face).