Originally Posted by
Radeghost
Frostmourne was supposedly crafted from the ice from the most distant corners of the Twisting Nether. Frostmourne was a part of the Frozen Throne, it was not forged by Nathrezim, it was created by the Lich King Ner'zhul.
The Frozen Throne was crafted from Twisting Nether ice. Nothing ever stated that Frostmourne was created from that ice. It's a plausible conclusion given the original WC3 lore, but Rise of the Lich King retconned the dialogue from WC3 about the Ner'zhul creating Frostmourne.
vs.
Tichondrius seemed not to notice. He pointed to Frostmourne. “The runeblade you carry was forged by my kind, long ago. The Lich King has empowered it to steal souls. Yours was the first one it claimed.”
--Rise of the Lich King