The Legend of Prince Valiant

S02:E38 - The Gathering Storm 

Valiant is crowned King, but Camelot is in deep trouble. The peasants are fleeing, fearing that they will conquered by Mordred. Morgana, Arthur's evil sister, is in league with Sir Kay, a traitorous knight of the Round Table. Morgana has prepared a poison which she applies to Sir Kay's hand (to which he is supposedly immune), so that Sir Kay can poison Bryant and Gawain disabling the battle leaders of Camelot.