The portal opening must have been us arriving. But since the King is a member of the Divine Council, maybe he will help out here, after all, it was them, at the suggestion of their Lycan member, who sent Karl and Elder Song here. Speaking of which:
"Librarian! I knew you wouldn't actually be dead." I hear an advisors voice over the din of battle, and see Elder Song giving him an annoyed look even as both continue to fight. Dozens of Divine Realm Cultivators are here now. The Lycans followed Beta John through, the King brought his Bodyguard plus a few curious advisors, and it seems they're calling on even more.
High level Nephilim and Lycans are still emerging from the Portal, more than I thought were in the castle, and are spreading out in every direction. Not just to secure the area, they're going beyond the horizon as well.