Suddenly, somehow, this situation became personal.

Sombra is back after being banished by Celestia and Luna over a millennia ago. The Doctor knows that Princess Celestia wants Twilight to find a way to protect the Crystal Empire, but he's afraid that she might not be able to. King Sombra has grown strong during his exile, and the Doctor doesn't know if he's now immune to the affects of the Crystal Heart or not.

Only time will tell.

Because if it fails, he will be the only thing will be standing between the tyrant and the Crystal Empire if it does.

(Note: This takes place during The Crystal Empire Part 1 and Part 2. Not word for word. I'm kinda rewriting it in order for it to run smoother in a story format, but it will follow the plot of the two episodes before getting considerably darker, and will contain some dialog from the episodes.)