Does a ghost gain a familiar if it uses a Ring of Spell Storing + Find Familiar?

A ghost takes possession of a humanoid. Humanoid possesses a Ring of Spell Storing. The ghost uses the Ring of Spell Storing that contains at least one Find Familiar spell. The ghost-humanoid combination now has a familiar (congratulations)!

Ghost leaves / ends possession / then goes to the Border Etherial, as per RAW

Who does the familiar follow? Does it stay with the physical humanoid / ring combo-duo or does it go with the ghost that first leaves the body and then goes off to another plane of existence?