File:Frostmourne first concept.jpg

Summary
"The First Frostmourne Concept, Originally Called 'Frostmourn'" Sam "Samwise" Didier, c. 2000 Pencil on Paper Warcraft III: Reign of Chaos

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From the source: "'Frostmourne was a cursed runeblade of unimaginable evil, capable of imprisoning the souls of those slain by its blade. It held part of the Lich King’s consciousness and linked him with Frostmourne’s wielder, Prince Arthas Menethil, during the Third War—which concluded with Arthas becoming the Lich King himself.'"

Source
BlizzConline, Warcraft Art Gallery:
 * Website
 * File link