Leonardo painted The Last Supper, which has come under much scrutiny since the book and film for The Da Vinci Code came out.
In the picture you don't see the Holy Grail as one specific cup they all drank from, you see that each man has his own cup. Also the young man to the right to Jesus is theorised to by John. Which makes you ask why his face is hairless as Jews did not shave their beards the way the Romans did. The answer is that this is not John, but Mary Magdelene.
Further theory is that the Grail itself was never a cup at all, but refers to MM herself. But that's a whole other story.
