Triangle Holocaust

The apocalyptic event that would signal the end of the Ancients' heirs. This has been interpreted to mean the destruction of the last living Ancients, or the end of human civilization, which would be succeeded by their own heirs. The Triangle Holocaust gets its name from the three Apocalypse Lords, who's united power brings about the event.

Prophecy
The Triangle Holocaust was foretold to bring an end to the Ancients' successors, humans. The details of this occurrence were never very specific, but seers warned that three Apocalypse Lords would unite to bring about this catastrophe, and that if the last Ancient prince were consumed by Tyat'Naghra the Time Serpent, it would mean an immense catastrophe that would rock the entire universe.

Different interpretations of the prophecy existed within the Church. Ancients who had consulted with an entity believed to be the Dark Goat interpreted the Triangle Holocaust's titular three apocalypses to be circumstances, rather than individuals, and the names of these circumstances included famine, war, disease, depravity and tribulation.

Those who attempted to discover the conversation that took place between a group of Ancients and the Former Artificial Intelligence were confused by tales of a three-pronged apocalypse, and various other interpretations led to the Church announcing the end of the Ancient civilization itself would come via three harbingers.

Participants
Only three Apocalypse Lords confronted Lossoriawath the last Ancient prince, while also fighting the Time Serpent. These were Foray, the IAU who was able to control matter thanks to the S'cha-ckl'ueu Arc, Kate, a female Ancient/human hybrid who manipulated space, and their counterpart, human male John Beckett the living time machine.

The End of the World
Originally, the Guardian was considered an Apocalypse Lord as well due to the curse of the Old Being he killed allowing him to manipulate energy fields, and completing the set (time/space, energy/matter). However, in defiance of the prophecy, the Guardian stayed behind, using his cursed power to overcome the fleeing Lossoriawath's barriers and allowing John to bring Kate and Foray to the future and chase down the Ancient prince.

As Lossoriawath fled in time, he was attacked by the Time Serpent, leaving him stranded in the far future. When the Apocalypse Lords arrived, he was able to fight them off for some time with his Immortality Gauntlet. He attempted to flee to the Temporal Matrix, forgetting that Tyat'Naghra had vanished near the stairway some time ago. As he ran up the stairs, Tyat'Naghra came out of the past and devoured him. Together, the Apocalypse Lords used their combined power to seal themselves and the Time Serpent within the S'cha-ckl'ueu Arc, which remained aboard the Temporal Matrix until it was recovered by the Guardians

The Guardian noted that this action took place in the far future, and so rather coincided with the end of humanity rather than directly causing it. However, Tyat'Naghra had devoured Lossoriawath and no calamity had occurred yet. This makes the Guardian uneasy for some time, and he keeps the S'cha-ckl'ueu Arc safely aboard the Temporal Matrix.

Fulfillment
After the Guardian's death at the hands of the Ravager, the Ravager entered the Temporal Matrix and began traveling across time. While doing so, he curiously touched the S'cha-ckl'ueu Arc and released the power within, which united with the two Impossible Machines, and proceeded to destroy the first six universes after the Fracture and create a Disrupted Timeline.