After the new S-Class debuted last year, Mercedes is preparing its smaller C-Class sibling for its long-awaited debut. Prototypes of the new C-Class have been spied for several years now, so the luxury sedan's debut has been a long time coming, to say the least. Nothing official has been announced yet, but Mercedes is expected to unveil the new C-Class later this month.

Ahead of its debut, Autocar has uncovered new details about the compact luxury sedan during a recent test drive of a prototype with Mercedes development boss Christian Fruh behind the wheel. Visually, the new Mercedes C-Class isn't a dramatic departure from its predecessor, which isn't a surprise considering the current model is one of the German automaker's best sellers.

While the design looks very similar, every panel has been altered, new "power domes" adorn the hood, the wheel arches are longer, and the front track is wider. Compared to the outgoing model, the new C-Class saloon is also 2.5 inches longer with a 1.18-inch longer wheelbase. As a result, the cabin is more spacious, with 0.9 inches more rear legroom and 0.5 inches more headroom.

Inside, the cabin is heavily inspired by the new S-Class, with a digital instrument display dominating the dashboard, a large central touchscreen, and four central air vents that glow in shades of blue and red. A new augmented reality display will also carry over from the S-Class, controlled by the latest MBUX system. Like the S-Class, the cabin will be devoid of physical switches and dials - only the hazard lights are activated with a physical button.

Underpinning the new C-Class will be the same Mercedes' Modular Rear Architecture platform as the S-Class with more extensive use of steel and a new 48V electrical architecture. As for the powertrains, every engine option will be a mild-hybrid four-cylinder unit since Mercedes' new straight sixes would have required a longer engine bay and front overhang. The C300 4Matic will pack a 2.0-liter turbo gasoline engine with a 20-hp integrated starter-generator and an overboost function providing an extra 27 hp for up to 30 seconds.

This unit will be paired with a nine-speed automatic and a four-wheel-drive system as standard. Europe's diesel plug-in hybrid models will also boast a higher 25.4-kWh battery capacity enabling an electric range of 62 miles, more than double that of its predecessor. These improvements suggest the new C-Class will be a worthy successor to the current model, but we'll find out more details when it hopefully debuts later this month.