Knowing his master, it was impossible to talk his way out of this battle. The only way was defeat and torture. Seeker could not afford to be questioned by the Realm King for too long.
He knew that if he had allowed the Realm King to take him and question him, it would be days and days after it happened. The Realm King would keep Seeker a prisoner and try to outdo what Seeker has built. In short, the Realm King won't ally with Seeker's armies.
The Realm King was so skeptical that even Seeker never heard of the fact that his master knew who the Lost Primordial was in his previous life. But now, Seeker deduced that his master was, in fact, one of the essential pieces set by the Progenitor.
With the Realm King's abilities, he could sense powerful entities' rough locations in this world. But because of the grim warning, the Lost Primordial left behind, and the orders to never seek each other out would make it hard for them to unite.