‘You hurt me, you corpse-master’s lapdog.’ The last vestiges of Fulgrim’s humanity melted from his face as it transformed into a mask of pure hatred. ‘No one hurts me. No one beats me!’

He wrapped his tail around his brother primarch, constricting him with such force that his armour plate began to crack. Casting aside one sword, Fulgrim reached down and grasped Guilliman’s head.

‘You wanted to face me, so face me!’ he said, wrenching free Guilliman’s helmet, exposing his naked flesh to the air.

The stink of his corrupted brother made Guilliman gag. His head swam as the daemon primarch’s scent invaded his nose and throat, unmoderated by his battlehelm’s systems.

‘Pathetic!’ cried Fulgrim. He uncurled, flinging Guilliman aside. His wounded arm was already healing, crackling warp energies working in tandem with his primarch’s physiology to make him whole again. He conjured swords from poisoned mists to fill his empty hands and flew at the Master of Macragge.

Guilliman staggered upright, gasping. Every breath poured more of Fulgrim’s lethal perfume into his lungs, a poison so potent that it taxed his superhuman body. He parried, and parried again, but he could land no counterstrike and was forced back up the stairs.

A blow flung his arm wide. He never saw the blade that cut him coming.

A cold kiss across his throat, followed by searing agony. Arterial blood sprayed from his ruined neck. He clamped his hand to the wound, but it gaped beneath armoured fingers, and the blood would not stop. Poison crawled in where his blood flooded out. Already it affected him, numbing his lips first and making his eyes heavy. With supreme effort, Roboute Guilliman raised the Gladius Incandor for the last time.

‘How?’ he mouthed. His vocal cords were severed. Blood spilled from his mouth in place of words.

‘I see the mark of Kor Phaeron’s athame.’ Fulgrim swayed as he approached. ‘He could never turn you, but the cut he inflicted is a scar on the warp that could never heal. It is as great a weakness as your rectitude.’ Fulgrim smiled with lips coated in poison paint. ‘Or I should say was. Here the Avenging Son meets his end.’

He smashed at Guilliman’s sword so hard it flew from his limp grip into the heaving battle. Fulgrim raised his swords for the killing strike. ‘Say hello to father for me.’

A storm of fire blasted down the stairs, bolt-rounds streaking by, followed by burning streams of plasma. Fulgrim screeched. The unearthly field that shielded him shrieked and flickered, splitting his image. He screamed as a blaze of incandescent gas pierced his protection and burned his side.

‘The primarch! To the primarch!’ roared Captain Andros in anguish.

Guilliman sank to his knees, unable to speak. His perceptions became fragmentary. Warriors in blue threw themselves at the reeling daemon prince, only to be carved up into red chunks in in mid-air.