We've seen BMW testing the next-generation 3 Series couple of times in the past year or so, but its high-performance M3 sibling has remained elusive up until now. One of our spy photographers caught this example out testing, and, based on these shots, the visual differences between it and the garden-variety 3 Series will be quite modest.This M3 will of course have some of the model's signature cues. We can see that it will have quad exhaust tips and fatter fenders. We can also just barely make out a fender vent. That vent now looks a little higher up and more slender than the current one. The wheels hide some seriously big binders, too. And, while it may be more of a general performance car trait than one exclusive to the M3, we can see that it has a rear lip spoiler and that the front bumper has much larger grilles. The exact shape of the grilles are obscured, but they must be larger since there are bigger openings in the camouflage than on regular 3 Series prototypes.Besides these details, this M3 looks very much like a plain 3 Series.The main kidney grilles don't look differently shaped, though they do appear to have slimmer slats for air flow. The hood doesn't appear to have any major bulges, either. The mirrors, which have often been unique on M3s, are the same as other prototypes.We recently saw a normal 3 Series that had production-ready equipment, so we expect that it will appear sometime next year as a 2019 model. BMW is clearly working on the M3 in conjunction with the regular 3 Series, so we wouldn't be surprised if the M3 makes its debut alongside the normal car, or comes out a few months later. Either way, it will probably show up next year.