Mercedes-AMG is readying a new plug-in hybrid version of its GT 4-Door Coupe.

Our spy shots show a prototype of the AMG sedan with a concealed flap on its rear fascia, located just below the taillight on the right. On the corresponding rear fender is the regular filler cap.

When the Mercedes-AMG GT Concept bowed in 2017 as a preview of the GT 4-Door Coupe, the striking show car packed a powerful electrified V-8 under the hood. So far such a powertrain hasn't taken shape but that is now about to change. In fact, AMG has already teased it, meaning a debut later this year is likely.

2021 Mercedes-AMG GT 73 EQ Performance 4-Door Coupe spy shots - Photo credit: S. Baldauf/SB-Medien

2021 Mercedes-AMG GT 73 EQ Performance 4-Door Coupe spy shots - Photo credit: S. Baldauf/SB-Medien

The electrified sedan will be positioned as the range-topper in the GT 4-Door Coupe lineup, similar to how Porsche's Panamera and Cayenne also feature plug-in hybrids as their top option. Expect the AMG to be called something along the lines of GT 73 EQ Performance 4-Door Coupe; EQ Performance is the new performance label of Mercedes-Benz's EQ sub-brand for electrified cars and also features on the automaker's latest Formula One car.

No specs have been confirmed but rumors point to the powertrain mirroring the setup in the original GT concept, which AMG quoted at 805 horsepower. Specifically, AMG said the concept featured a 4.0-liter twin-turbocharged V-8 married to a powerful electric motor capable of driving the car on its own. Currently, the GT 4-Door Coupe range tops out with the GT 63 S, whose output is 630 hp.

Although any GT 4-Door Coupe plug-in hybrid will likely weigh more than the GT 63 S, it should handily outrun it if we see anything like the 805 hp of the concept. With such an output, expect the super sedan to sprint to 62 mph in 3.0 seconds or less. The GT 63 S has already been clocked at 3.2 seconds.

2021 Mercedes-AMG GT 73 EQ Performance 4-Door Coupe spy shots - Photo credit: S. Baldauf/SB-Medien

2021 Mercedes-AMG GT 73 EQ Performance 4-Door Coupe spy shots - Photo credit: S. Baldauf/SB-Medien

The plug-in hybrid system will eventually filter across to other high-end models in the AMG lineup, filling in for the previous V-12 option that bowed out in 2019.

Eager buyers should expect a premium price for the extra performance the powertrain brings. The AMG GT 63 S already starts at $159,995. For this kind of money, buyers could also opt for the Porsche Panamera Turbo S E-Hybrid or the battery-electric Porsche Taycan Turbo S.

AMG doesn't have an answer to the Taycan just yet but CEO Tobias Moers in an interview last September said an electric AMG was in the works. Timing of the vehicle isn't clear but it is expected to be based on Mercedes' new dedicated EV platform that debuts this year in the EQS sedan.