Emperor's Children - Horus Heresy: Certain members of the Inquisition who have studied the fragmentary Imperial records of this time now believe that the Laeran daemonsword began to exert a powerful Chaos influence over Fulgrim, and that the Emperor's Children forces he had deployed against the Laer may also have been tainted by their exposure to the concentrated Chaos corruption of that serpentine race, who had fully sworn themselves to the service of Slaanesh.Even while wrestling with his own Chaos taint, the primarch of the Emperor's Children soon found himself at the center of the events that would bring on the Horus Heresy.Fulgrim met with the renowned Aeldari Farseer Eldrad Ulthran of Craftworld Ulthwe on the Maiden World of Tarsus, in which the Farseer attempted to warn Fulgrim that Horus had been wounded by the Chaos artefact blade known as the Kinebrach Anathame at the hands of Eugen Temba, the Planetary Governor of Davin who had fallen to the influence of the Plague Lord Nurgle.The wounding had allowed the Chaos Gods to gain a purchase on the Warmaster's soul and he was already turning to their service as he recuperated from the nearly-mortal wound the Kinebrach blade had given him at the hands of Temba on the Nurgle-corrupted moon of Davin. Fulgrim reacted with violent outrage at the Farseer's accusations due to his close friendship with his brother Horus, as his bond with the Warmaster was second only to that he shared with Ferrus Manus, the Primarch of the Xth Legion.This outrage was further enhanced by the influence of Fulgrim's daemonblade, which wanted the Primarch to reject the Aeldari's truth and it led Fulgrim to launch an unprovoked and furious attack on Eldrad and his retinue alongside his Emperor's Children Captains and his personal Phoenix Guard. In the battle that ensued, the Emperor's Children slew both the revered Aeldari Wraithlord Khiraen Goldhelm and a potent Avatar of Khaine, which forced the Farseer and the other Aeldari troops to sorrowfully withdraw, as they realised that Chaos had already claimed yet another of the Mon-Keigh 's Primarchs.Yet they had succeeded in killing all of Fulgrim's elite personal Phoenix Guard before their departure. Believing the Eldar had proven themselves a treacherous race that sought to divide and conquer the Imperium by spreading such lies about its leaders, Fulgrim, again under the increasing influence of the daemonblade, ordered the destruction by the 28th Expeditionary Fleet of several other beautiful Eldar Maiden Worlds using hideous virus bombs.Whilst the exact timing of this meeting remains unknown in Imperial records, it is known that Fulgrim soon met Horus in person after the Aeldari had provided their warning about the Warmaster's turn to Chaos, and Fulgrim demanded a personal account of his actions. Instead, Horus, deploying every ounce of his immense charisma, proved able to sway Fulgrim to his cause and the service of the Ruinous Powers.Fulgrim's respect for Horus allowed Chaos to find its own way into Fulgrim's heart, destroying Fulgrim's once rock-solid loyalty to the Emperor, and replacing it with the burning desire to destroy the man who he now believed held humanity back from the perfection Fulgrim so craved and that Horus convinced him only the Chaos Gods could truly provide.Only when Mankind had fully embraced Chaos could it know true perfection, Fulgrim came to believe, and the Emperor and His false Imperial Truth stood directly in the way of his and the rest of humanity's attainment of that perfection. In recognition of the trust Horus put in his brother, he gifted him with the potent Chaotic blade known as the Kinebrach Anathame. Only the two brothers shared the secret of the poisoned blade's true power, as it was the weapon blessed by the Plague God Nurgle that had almost killed Horus on Davin's feral moon.Fulgrim was next ordered by Horus to meet with Ferrus Manus, the Primarch of the Iron Hands Legion and Fulgrim's greatest friend amongst his brother Primarchs, aboard his flagship the Battle Barge Fist of Iron in the hope that he could be swayed to the side of Horus and the other Traitor Legions who now served Chaos. Fulgrim had sent the bulk of his Legion and the 28th Expeditionary Fleet on to meet Horus and the 63rd Expeditionary Fleet in the Istvaan System while he and a small force aided the Iron Hands' 52nd Expeditionary Fleet in retaking the world of Callinedes IV from Orks.Great bonds of friendship and brotherhood had long existed between them, and Fulgrim felt that he could convince Ferrus of the righteousness of Horus' cause. Fulgrim's hope proved disastrously wrong and the meeting of the two Primarchs in Ferrus' private inner sanctum in his flagship's Anvilarium did not go well, as Ferrus was outraged that his brothers would turn against their father the Emperor.The meeting ended in violence as The Gorgon made his difference of opinion over continued loyalty to the Emperor known to the Phoenician with his weapons, and he was determined to stop Fulgrim's betrayal of the Imperium before it could begin. Ferrus used his silvery necrodermis hands to destroy Fulgrim's Power Sword Fireblade, but the explosion knocked him out.Fulgrim intended to kill his brother with his own weapon, the warhammer Forgebreaker, but proved unable to kill his oldest friend despite the promptings of the Slaaneshi daemon that now throttled his soul. When Fulgrim emerged from Ferrus' inner sanctum, he gave a signal to his Phoenix Guard who instantly beheaded all of the Iron Hands Morlocks Terminators who served as Ferrus Manus' bodyguard with their Power Halberds.The Emperor's Children also nearly slew the Iron Hands' First Captain Gabriel Santor. Fulgrim successfully fled the Iron Hands' expeditionary fleet in his personal assault craft, the Firebird, when he ordered his flagship, the Battle Barge Pride of the Emperor and its Escorts, to open fire upon the ships of the 52nd Expeditionary Fleet. This surprise attack crippled them and provided a distraction while Fulgrim and the forces of the IIIrd Legion fled into the Warp to rendezvous with the rest of their 28th Expeditionary Fleet in the Istvaan System.With their allegiance now settled and their path forward determined, the Chaotic corruption of the Emperor's Children spread quickly throughout the IIIrd Legion, from Fulgrim to his chief lieutenants, the two Lord Commanders of the Legion, and then to its company captains and squad sergeants and finally to all but a small minority of Emperor's Children Astartes who followed the dictates of Slaanesh rather than remaining loyal to the Emperor. The IIIrd Legion's once-laudable quest for excellence and perfection had been corrupted into a desire to achieve perfect hedonism and constant, self-absorbed, sensual excess.