1963 Corvette Sting Ray Split-Window Fastback: And Where Exactly Did That Come From?

I don’t mean the general design of the ’63 Corvette’s fastback; as early as 1957, the very advanced but still-born Q Corvette prototype already sported a fastback, as well as other later previews of Sting Ray styling. But that fine crease down the middle, and the controversial decision to split the rear window (for one year only? I don’t remember any Corvette or other GM prototypes sporting that. Where exactly did that come from? And then it popped in my head: Bill Mitchell made regular trips to Europe, to scout for ideas, among other things. He must have run into one of these somewhere in his travels:

Got a better explanation?