The King and Arthur
All of the vampires, as soon as they saw the first two men appear from the blood dome, they knew who would be following after them. The reason, because the king never travelled anywhere without his two royal guards.
The royal guards would be selected from the leaders of the past. Once the election for the next king was over. They were free to choose two guards from the current section of leaders.
One would usually choose the strongest of leaders of that generation and most loyal to protect the king. Their power was often above an average leader.
Although Vorden, Quinn and the others didn't know what the vampire king looked like or who he was. They could tell as soon as he had stepped in. He had this sense of superiority around him. As if he was meant to be in that place.