When the Mercedes-AMG GT sedan concept bowed in 2017, the car was said to boast a powerful electrified V-8 under the hood. So far, such a powertrain hasn't taken shape, but it appears that will soon change.

A Friday report from Autocar showed spy photos of a curious AMG GT 4-Door Coupe undergoing testing. When the photographer peeked under the hood, he or she spotted an electrical system that looked like one used in plug-in hybrid vehicles. Per the report, the photography said the car drove off silently, which means it has enough electric power to move without the aid of the engine for at least a short distance.

2019 Mercedes-AMG GT 63 S 4-Door Coupe

2019 Mercedes-AMG GT 63 S 4-Door Coupe

It's very possible this AMG GT 4-Door Coupe model will mirror the GT sedan concept's hybrid powertrain, which Mercedes quoted at 805 horsepower. Specifically, Mercedes said it featured a twin-turbo 4.0-liter V-8 married to a powerful electric motor, which could also drive the car on pure electricity. Autocar's sources claim the car will go 31 miles on electricity alone with a full charge. Consider this model a rival to the Porsche Panamera Turbo S E-Hybrid.

The report also speculated the car will wear the AMG GT 73 4Matic name, which Mercedes-Benz recently applied to trademark. Currently, the AMG GT 4-Door Coupe tops out in 63 S trim with its twin-turbo 4.0-liter V-8.

2019 Mercedes-AMG GT 63 S 4-Door Coupe

2019 Mercedes-AMG GT 63 S 4-Door Coupe

Although the AMG GT 4-Door Coupe plug-in hybrid will likely weigh substantially more than the GT 63 S, it should handily outrun it. With more than 800 hp, Autocar claims the rumored GT 73 4Matic will sprint from 0-62 mph in under 3.0 seconds. The GT 63 S will do the same drag in 3.2 seconds.

Eager buyers should expect a premium price for the extra performance. The AMG GT 63 S already starts at $159,995. The price of entry into the GT 4-Door Coupe lineup (it's really a hatchback) is $99,995, which nets buyers a turbocharged 3.0-liter inline-6 paired with Mercedes' 48-volt mild-hybrid system.