BAN'S CROWN

When Gwenbaus decided to stay behind in Britain with his princess in the Forest Perilous [or Forest Perdue], his brother King Ban of Benwick left his crown with them. Gwenbaus enchanted the forest grove.

The crown may not have been magical in itself, but it gained a magical association; the enchantment was not broken until Lancelot came, sat in the chair, and wore the crown.