Over the past several months, spy photographers have captured a series of mysterious images of some X5 prototypes. Speculations have ranged from an M version of the X5 to a sportier X5 5.0is to a mule for an upcoming V10-powered X6. But, if the latest report is accurate, the mystery has been solved.

According to BimmerFile, BMW isn't keeping true to its word and the German automaker is not readying an M version of the X5. And while a V10 powerplant may be in the X6's future, we aren't looking at the test mule for it. Through the process of elimination, that leaves us with a prototype for the BMW X5 5.0is.

BimmerFile says the new X5 5.0is will carry on in the same vein as the previous X5 4.8is — a step above the standard SUV in sportiness but still not qualified to wear the M emblem. Underhood, the X5 5.0is will use the same twin-turbocharged V8 found under the hood of the BMW X6 xDrive 50i — tuned to produce 407 horsepower. However, it has been reported that BMW is having some lag issues with the turbocharged engine, which could explain the extra development time.

So while it looks like we have an answer to the X5 mystery, just remember that nothing is official in the auto industry until you see it on the road.

X6-style front treatment?

While prior prototypes had some styling changes, the headlight design remained pure X5. On this newest prototype, the headlights appear to have been switched out with X6 headlights.

This latest prototype also features a new rear treatment. Earlier prototypes used the standard X5 rear valance, mocked-up to accommodate its new M-style quad exhaust set-up. The X5 shot yesterday, however, gets a new, larger rear bumper that wraps around to the middle of the rear wheel well. The rear fascia on the new prototype looks like a more-finished production application compared to the initial test mules.

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