The Great Truth is a massive secret kept from all races who reached their space ages from the mid-Ancients era onwards. The Great Truth is said to be one of the primary pieces of knowledge from Ancient times, although the exact details of it are such a closely-guarded secret that it is not known what it actually entails. However, it is considered to be of equal importance to the Origins of the Chaos Legions and The Unspoken Words (the truth behind the creation of the UFCL). Species that know and have "always" known the Great Truth are or were the Centro, Crozo, Cthalon, Dragoon, Mnemosyne, Permitted (who no longer care about its content one way or another as they refuse to involve themselves in any way, shape or form with any sapient matters outside of themselves), Sculptors, Starriders (both light and dark), Vggdrassil, Voiasenso and Yggdrassil.
In 2874 AD, the Voiasenso revealed the Great Truth to the chaotic Gohd and gave them only 4 years to clean up their act or be eradicated in light of the knowledge they were given. The knowledge affected the Gohd enough for them to drop their plans to destroy the Human race. The Gohd however were shocked and disgusted by the knowledge contained in the Great Truth and when asked about it have acted violently or embarrassed at the very notion of the other party bringing it up.