Episode Ardyn Prologue is an anime Square Enix is producing as an introduction to Final Fantasy XV: Episode Ardyn, which at the same time is the last DLC the game will be getting after the cancellation of the other three planned content drops.
The first King of Lucis is somewhat resentful, and that's not good when you're 2,000 years old. The anime is supposed to give background to these feelings and his search for revenge later in the game.
The teaser below sets the mood, mentions his brother Somnus if we hear correctly, and closes with a very Castlevania-ish shot. What do you think of this story and character?