Harmonized Trio // Brainstorm

A preparation card is a creature card in every zone. For example, while it's in your graveyard, Emeritus of Ideation is a blue creature whose mana value is 5. It can't be the target of Zealous Lorecaster's triggered ability ("When this creature enters, return target instant or sorcery card from your graveyard to your hand.").

While copies of spells in zones other than the stack cease to exist when state-based actions are checked, this does not apply to copies of prepare spells in exile that were created as a creature became prepared.

Only the current controller of a prepared creature can cast the copy of its prepare spell in exile. It doesn't matter who owns that creature or who controlled it when it became prepared.