The battle between Rui and King Albus was the most important battle of all, everything hinged on it. Although the Ferendul coup forces led by the former king of Ferendul had gained a small measure of Rui's capabilities and had been impressed, it was not strictly enough to say that Rui would definitively win against King Albus.
When Farun heard that Rui had openly challenged his son, he couldn't help but grow immensely upset. He had hoped that Rui would exploit the element of surprise to the absolute maximum, gaining an advantage early on in the battle. Ideally, he hoped that Rui would kill Albus before the latter could tap into the power of the Senior Realm, but he knew that Martial Seniors could not be killed in such a manner.
The worst outcome, however, was completely surrendering his element of surprise and evening out the battle. Now the battle truly could go either way, becoming a variable that Farun could no longer control or predict.