Have you seen this Buddleja?

I'm looking for more information on a lost hybrid of B. davidii/forrestii called Buddleja X 'Hotblackiana'. Has anyone ever seen this plant? I've seen the Wikipedia page, and the reference is wrong, as it doesn't mention the Buddleja at all.

I have a plant labelled B. limitanea, origin Longstock in the distant past, which is different from the listed cultivar and might be the hybrid. I've contacted Longstock National Collection, and the trail has gone cold. Here is photo of the putative hybrid:



Thanks for any information or leads.