Her Words Are My Words

After leaving the prison, William went to the Royal Palace that was located at the Capital City of the Demon Realm, Astryae.

All the Patriarchs that had survived the war and the newly elected Patriarchs who took over the management of their respective clans—after their Patriarchs had died in the war—gathered in the Royal Palace because the Half-Elf wanted to fully consolidate his authority, and ensure that no seeds of rebellion, or resistance, would emerge from their hearts.

Surprisingly the Patriarch of the Gremory Clan, Alvah survived the war. 

William gave the old patriarch a side-long glance, making the latter flinch as if the Half-Elf had spat on his face.

When the Half-Elf went to the North of the Demon Continent to deal with the Gremory Clan, he had every intention to wipe them off the face of the world.