If it's as tall as that I'm wonderng about some close relative of I. orientalis. Not sure of the distribution of that species. It doesn't look quite like it - no yellow on the falls for instance - but worth a thought perhaps. It would always be helpful to see the foliage when trying to identify irises, and, indeed, the whole plant.
Now I've had a better look, there IS some yellow well into the haft it seems. So I would suggest I. orientalis or a species close to that. Spuria section anyway. Formally known as I. ochroleuca.
