Posted: 13/05/2015 at 21:01
I think the clematis is "the president" and exactly the same happened to mine. The leaves went black then the whole thing wilted when it was in flower. At the time I thought it was wilt and cut it to the ground. I however believe it may have been either slugs damaged the stems at base level or the window cleaner damaged it climbing over the fence as when I cut it down the stems at the base had their bark stripped away.
Mine has since recovered however I am sure other people will give better advice.