Mercedes-Benz in April unveiled a new generation of its GLS full-size SUV, and once again there will be high-performance variants from Mercedes-AMG.

Our latest spy shots reveal a prototype for one of the upcoming AMG versions, likely to be a new GLS63.

We know this is the AMG version of the new GLS because of its protruding Panamericana grille design, which features on the latest AMG models like the GT 4-Door Coupe and G63.

2020 Mercedes-Benz GLS-Class

2020 Mercedes-Benz GLS-Class

The prototype also sports more intakes in its front fascia compared to the regular GLS, and in the rear fascia can clearly be seen AMG's signature square-shaped exhaust tips. There's also no missing the massive brakes the prototype is wearing, as well as its very wide rubber.

Under the hood of the GLS63 should be a 4.0-liter twin-turbocharged V-8 paired to a 9-speed automatic and all-wheel-drive system. A 48 mild-hybrid system should also form part of the equation.

The mild-hybrid system, which already features in the regular GLS, is essentially a beefed-up starter motor that can aid the engine when needed and recover energy under braking and coasting. In the GLS63, we could also see the mild-hybrid system used to power an electric compressor.

2021 Mercedes-AMG GLS63 spy shots - Image via S. Baldauf/SB-Medien

2021 Mercedes-AMG GLS63 spy shots - Image via S. Baldauf/SB-Medien

Expect output to be higher than the outgoing GLS63's 577 horsepower and 561 pound-feet of torque.

A tamer GLS53 with an inline-6 should also be in the works. We could also see at some point a GLS73. This one would feature the 4.0-liter twin-turbo V-8 paired with a more powerful electric drive system for an output approaching 800 hp. Such a configuration was previewed in AMG's GT sedan concept unveiled at the 2017 Geneva International Motor Show.

The new GLS arrives in dealerships late this year as a 2020 model. The GLS63 should arrive shortly after the regular model, possibly for the 2021 model year. Also in the works is an ultra-luxury version from Maybach.