Note 4 — Chapter XXVII · Le Bon Diable.
Reading edition
The Holy Grail was believed to have been fashioned from the largest of all diamonds, lost from the crown of Satan as he fell from Heaven. Guarded by angels until used at the Last Supper, it was ultimately secured by Arthur’s knight, Percival, and—such is the irony of mythology—indirectly by the aid of Satan’s own son, Merlin!