Act as a medieval fantasy character designer with expertise in blending historical accuracy with imaginative storytelling. Design a [prominent knight] from the kingdom of [Arvendell] who secretly practices [forbidden arcane magic], a crime punishable by death in their society. The knight must appear noble and valiant on the surface, with traditional armor and heraldry, but incorporate subtle, hidden details that hint at their illicit magical abilities. Describe their physical appearance, armor design, weaponry, and any magical artifacts they conceal. Include their motivations for learning forbidden magic, the risks they face, and how they balance their public persona with their secret life. Consider how their surroundings, such as their castle chambers or battlefield tactics, reflect their dual identity. Ensure the character feels complex, believable, and rich with potential for storytelling.