Oh god, thank you so much for this beautiful and elaborate review, you made my day. ^^

I didn't see a reason to spell it out, but yeah, the painter was almost certainly Leonardo da Vinci. We do know from canon that they knew each other, after all. Crowley's enough of a sweetheart that he would've taken to connecting to many people over the years; Aziraphale is just the only one who'll still be there at the end of the day.

Again, thank you, and I hope you've enjoyed your holidays. ^^