The Alchemist

The story is recounted by the protagonist, Count Antoine de C, in the first person. Hundreds of years ago, Antoine's noble ancestor was responsible for the death of a dark wizard, Michel Mauvais. The wizard's son, Charles le Sorcier, swore revenge on not only him but all his descendants, cursing them to die on reaching the age of 32.
The protagonist recounts how his ancestors all died in some mysterious way around the age of 32. The line has dwindled and the castle has been left to fall into disrepair, tower by tower. Finally, Antoine is the only one left, with one poor servant, Pierre, who raised him, and a tiny section of the castle with a single tower is still usable. Antoine has reached adulthood, and his 32nd year is approaching.
His servant eventually dies, leaving him completely alone, and he begins exploring the ruined parts of the castle. He finds a trapdoor in one of the oldest parts. Below, he discovers a passage with a locked door at the end. Just as he turns to leave, he hears a noise behind him and sees that the door is open and someone is standing in it. The man attempts to kill him but Antoine kills him first. His dying words reveal that he is none other than Charles, who actually managed to successfully fabricate the elixir of life, enabling him to personally fulfill the curse generation after generation.