This +1 magical sword (1d8) is made of cold-iron (+1d8 against elves of the Faërie), lined with gems, and inscribed with a curse against the Cold Prince.
Through some research in the Prismist's library, and after talking with Warwick at the Lucky Iron Smithy, and after comparing notes with Eggmar on his research, you learn that your sword is a prototype for a collection of weapons:
"During the war of the Hundred-Years Winter, several Eilvalorian princes made contact with the ancient long-lost dwarves who dwell deep underground. Together, it is said that they forged weapons capable of killing the Cold Prince. These weapons weren’t finished until after the war, however. They are untested and locked away in the ancient Eilvalorian treasure vaults, or so it is said."
Your weapon, a prototype for others, WAS tested in battle. In the final fight, when the trap for the Cold Prince was to be sprung, a warrior whose name is lost to time stabbed the cold prince with this very sword. While it wasn't powerful enough to kill him, it distracted him for long enough for the trap to be completed.