The Numista catalog calls this coin "ultra rare" ....but since there's only 1 .....shouldn't it be called 'unique"?
https://en.numista.com/catalogue/pieces5146.html
http://www.worldofcoins.eu/forum/index.php?PHPSESSID=52d97a187cf853e489ffe038c3611bc9&action=dlattach;topic=10999.0;attach=15738;image