Who is this Mystery Clematis ???

Who is this Mystery Clematis ???, originally uploaded by Campobello Island.

I suppose I must have planted this in my garden years ago but I don't think I have ever seen it bloom before. It is growing in a garden that I have allowed to go wild a mixture of shrubs, trees and perennials in a woodland setting along with wild flowers. This is sort of hidden behind some tall shrubs and is growing up a natural arch that the American Bittersweet has designed all on its own. It might have bloomed other years and I just didn't see it but I'm sure I would have remembered if I had, it is a stunner. If you know what variety this might be let me know.