Spy photographers have snapped a mysterious Bentley Flying Spur undergoing testing.

While the model doesn’t look terribly special at first glance, it features a charging port on the driver’s side rear fender. The gas cap, as you may recall, is located on the passenger side near the C-pillar.

This means we’re looking at a plug-in hybrid variant, but that’s not the only thing interesting about this prototype. As you can see, the model features a four-tailpipe exhaust system instead of the dual exhaust used on models with the twin-turbo 6.0-liter W12 that develops 626 hp (467 kW / 635 PS) and 664 lb-ft (900 Nm) of torque.

Also Read: 2020 Bentley Flying Spur Speed Will Likely Be A Plug-In Hybrid

While there’s speculation is the Flying Spur Speed, we’re not entirely convinced by the argument that the quad exhaust indicates this is the Speed. Four tailpipe exhaust systems are used on the current Continental GT V8 as well as the previous Flying Spur V8 and V8 S. It’s also worth mentioning that the Bentayga Speed, Mulsanne Speed and Continental GT Speed all had dual exhaust systems.

Whatever the case, we’re looking at a plug-in hybrid and it’s a tad different than previous PHEV prototypes that featured a dual exhaust system. That could suggest this is a performance-oriented plug-in hybrid, but nothing is official as of yet.

A lot of questions remain, but upcoming model is expected to share its powertrain(s) with the Porsche Panamera. If this is just a regular plug-in hybrid, it might feature a twin-turbo 2.9-liter V6 engine and an electric motor that gives it a combined output of around 456 hp (340 kW / 462 PS) and 516 lb-ft (700 Nm) of torque.

Of course, if this is the Flying Spur Speed it could use the same powertrain as the Panamera Turbo S E-Hybrid. That model has a twin-turbo 4.0-liter V8 and an electric motor that work together to produce 671 hp (500 kW / 680 PS) and 627 lb-ft (850 Nm) of torque.