[Bloody Sam Roberts]

What are the chances that he just painted over another picture?

'Slim' and 'None'.
It's a mural that Leonardo painted on a wall of stone...not a canvas.

[Sacajaweau]

Leonardo was NOT at the last supper and no matter what he created, it’s just his imagination. Anyone who reviews it is also using their imagination. The point is that it is enduring art. The tribute remains to the great artist who created it.