Uther stared at the flower in his hand blankly. So this was what Arthur had risked for that petty servant of his. He placed the Pendragon name in danger because of his reckless act to "save" a simple-minded boy.
He even disobeyed his own father. Uther specifically told him not to leave the castle. Instead, not only had he left the castle, but he had also encountered Nimueh, who possibly gave a hint to what really happened to his mother.
He continued to observe the flower in his hands. This was the flower his heir had risked his life for. If this flower never existed, that servant boy would have just died and would have been replaced within a couple of days. How dare his son disobey him just for this pitiful plant.
He crumpled the flower in his hands and watched as his son's face turned to pure horror.
"No!" Arthur screamed.
"You have to learn there's a right and a wrong way of doing things. I'll see you're let out in a week. Then you can find yourself another servant."
The king dropped the weak plant and walked out of the cell. Nobody was going to be in the way of his son's crowning, and nobody was going to stop the Pendragons from ruling longer.