Gaiaterra: Elysea's Conflict/The Ten Traitor Primarches

The Horus Heresy was, and still is, one of the greatest defeat the Heralds as they had still lost despite outnumbering the Coalition and the element of surprise, with the sole silver lining being that the Heralds now had Astartes to bolster their forces, with only ten (eleven if you separate the Alpha Legions Primarchs) out of the twenty Primarches having turned to Chaos in the war, whose legion now serves the Heralds today.

Trivia

 * With all Astartes in Gaiaterra being intersex the Primarches' genders are different from 40k, with four being male, three female, and four non-binary.
 * Horus, Angron, Konrad, and the 11th Primarch remain male
 * Magnus (Magna), Alpharius (Alphara), and Omegon (Omegan) now identify as female
 * Lorgar, Fulgrim, Mortarion, and Perturabo now identify as non-binary