Kingsbane (dagger)

Source
This item drops from Yogg-Saron in the 10-man version of Ulduar.

Trivia

 * In patch 3.1, King Llane is seen during Yogg-Saron's vision of his assassination. Yogg-Saron also drops two pieces of gear apparently tied to King Llane: Royal Seal of King Llane and Kingsbane. The former is his symbol of office, stained with blood from his assassination. The latter seemed to imply it was the weapon used to do the deed. It was later revealed that Garona Halforcen actually used The Kingslayers.
 * Kingsbane appears as a legendary card for the rogue class in the Kobolds & Catacombs expansion for Hearthstone, although its appearance is closer to that of The Kingslayers. Its flavor text reads: "But it has a soft spot for emperors."