Horus and the Emperor dueling shakes and hurts the infinite size realm which was Horus's ship

The arc of power goes wide. It scorches Loken and Leetu as it passes over them, and scalds their flesh inside their plate. It blasts a deep and molten trench in the floor of the Court. The infinite architecture of the Warmaster's sanctum shivers and shifts to repair its sepulchre-black form.
Horus thrusts forwards. Caecaltus strikes him again, from the right. The Warmaster smashes him aside without a second look, intent upon his son. The proconsul tumbles away, a discarded toy, praesidium shield shattered and Aquilon plate torn.
Loken gets to his feet as Leetu finds his. He turns to face his father. The Warmaster is an onrushing avalanche of darkness. The claws rise. Power wells to roast his son to cinders. The baleful lightning arcs out and envelops Loken and Leetu both.
They do not die. They stand, bemused, as the hate and power, black as Old Night and threaded with warpflux, crackles around them with an absolute vehemence, yet held at bay.
Horus lowers his hand, and the lightning stops.
He turns.
The Emperor lowers His hand, dissolving the mind-shield that prevented the immolation of His two warriors. He is standing. His golden breastplate is scorched black, and His cloak is charred. Blood runs slowly from His nose and the corner of His lip. His war-sword rises in His hand, and an asterism of white light flares like a rising sun behind His crowned head.
He moves towards His son with the lustral wrath of a supernova. Horus comes to meet Him with the atrocifying hunger of a black hole.
They clash, each landing blows simultaneously. The ignescent collision shakes the world. Chunks of black marble and broken buttress rain down from the quaked ceiling. Fractal surfaces break and shatter like porcelain. The high windows of the Court blow out in showers of coloured glassaic, letting in the red glow of the warp and permitting a giddying view of Terra, blistered and enflamed below.
The Old Four squeal in alarm, and then applaud. Father and son.
This is between them now.

- Siege of Terra, The End And The Death: Volume three