A continuation done with permission of a story by a friend on DA.
Read his story first or a good part of this won't make sense. The two parts can be found on DA.
http://fav.me/d5ubc08
http://fav.me/d5vngyg

Luna once more goes to be with the spirit of Jetfire, the love of her life from before her time as Nightmare Moon. He helps her to adjust to a world that still has yet to fully accept her, and brings her joy she ahd never known before. However, this joy also leaves her with an unexpected gift, one she won't know how to handle...and it leaves Celestia with a bit of a problem.
For one thing, the spell Luna's been using to spend time with Jetfire is a state secret for a very good reason. Meddling with the boundary between life and death is dangerous.
For another, Luan has been quite focal in her lack of interest in any stallions - or mares - of the present era, saying she will never love again.
So how is Celestia supposed to explain this?

Jetfire belongs to Irft4san on DeviantArt. The spell was also his creation. This plotline is mine. MLP:FiM belongs to Hasbro. Don't sue me.