|Lou, this is amazing and so are you for identifying it. I looked only at butterflies of North America. Since this was at a closed conservatory exhibition, and they take great care not to allow any butterflies to escape, I think it must have been brought as a pupa to hatch. I will try to contact them to see if they really do know that it is here and is a non-native species.
"Charaxes varanes" (6)