Frostmourne isn’t a Death Knight weapon, it was the Lich King, Arthas Menathil’s iconic weapon. Henceforth the 508ilevel Blood Death Knight with his loyal fox pet Renny, who’s exploits include completing a +2 Nokhud Offensive astride his Renewed Proto-Drake, didn’t wield Frostmourne at any point in his illustrious career. Lester the Paladin, Champion of Azeroth, did wield the actual Ashbringer, along with Fapfap the shaman who had Doomhammer, and Betty-Sue the Priest who had T’uure, Beacon of the Naaru. Henceforth did use the iconic Death Knight set of swords called the Blades of the Fallen Prince however! Coming up with crazy stupid scenarios and insane rationales on why any Death Knight would want to carry that weapon for any other reason than to be the Dollar Store wanna be Lich King is crazy. Even Bolvar didnt get it recrafted. He had his own iconic weapon forged and he was the second Lich King. You, Henceforth, are not the Lich King and carrying a replica of that weapon is ridiculous from any lore standpoint. Lester the Paladin still has the actual real Ashbringer in his closet though, and he will gladly let you polish it any time you come to visit.