Fal'inrush, Defender of Quel'thalas

Source
This item drops from the Lich King in the 25-man version of Icecrown Citadel.

Speculation
This crossbow would have been picked up by Arthas Menethil as he and The Scourge attacked Quel'Thalas to get to The Sunwell. It most likely belonged to Sylvanas Windrunner, although any high elf ranger may have used it.