Diamant. This brand crops up in East Germany and later in Belgium...Deutschland definitely preferred to let the outlying countries make the bikes they bought, maybe they just thought of bikes as being too Dutch, and not for them to bother about. I wonder where Mannesmann was based, maybe Austria? They produced a lot of the tubing for Italian and perhaps French companies that the consumer thought was pulling their own...I've heard of Oria, Excel, Falk as actually having some if not all of their tubesets drawn by Mannesmann...sure looks German to me.