Fulgrim against Ferrus Manus (Isstvan V)

At the drop site on Isstvan V, when the second wave of traitors struck the loyalists in the back, Fulgrim — already enslaved by the daemon of Slaanesh from the Laer blade — met his once closest brother, Ferrus Manus. In a furious duel Fulgrim struck off Ferrus’s head with the cursed sword, making the Gorgon the first primarch to die in the Heresy. For a moment he was horrified at what he had done, but then surrendered himself utterly to corruption and took Ferrus’s hammer, the Mountain-Crusher, to present it to Horus.