Magnus is my favorite character in Falling Kingdoms so far, so I'm giving you a quote from his POV.
Even without looking, Magnus felt his father’s gaze like a burning sensation down the length of his scar. A cool line of perspiration slid down his spine, even though he tried his best to look completely at ease.—page 110-111, FALLING KINGDOMS
King Gaius had a quick temper, and Magnus knew firsthand what it was like to be punished if he pushed too far. After all, he had the scar to prove it.