User blog comment:FairyRaven/Fairy Tail Chapter 389: The Twin Dragons vs. The King of Hades, Review and Commentary/@comment-2214433-20140620094147

"How does Minerva know that though...? >__> it's not like she stayed in Cube for a long time to know this stuff..." I'm guessing she overheard some conversations while being held in Hell's Core? She did react when Kyouka mentioned Fairy Tail, after all...