This Merlin sur la BBC photo contains
banc de parc, costume d'affaires, and costume d’affaires.
There might also be
robe costume, robe complète, frac, manteau de queue, queues, cravate blanche, cravate blanche et la queue, robe longue, tailcoat, tail coat, tails, cravate blanche et queues, habit, robe pleine, and queue de pie.
STORY: The song is about King Arthur's son Mordred, who was born between Arthur and his half-sister, Morgaine Le Fay. It's Morgaine chant to him; persuading him to kill his father, which he ends up doing. Basically that is the story