What's all this about?

Mercedes began making SUVs way back in 1997, with its original ML eventually morphing into the M-Class and thence the GLE. And, since then, five million customers worldwide have bought Merc SUVS, of one shape and another. Which must explain why Stuttgart is in such an SUV frenzy right now, because barely a day goes by without us getting some sort of new 4x4-type product from the three-pointed star.

Why do you say Mercedes is in an SUV frenzy?

Well, the aforementioned GLE has just evolved into its Mk4 shape, complete with the option of seven seats, should you want them. Both the GLC and GLC Coupe are in the process of being facelifted and AMG-ified. There's an all-new GLA inbound and, as if that weren't enough, Mercedes has even teased the idea of YET ANOTHER seven-seat SUV in the form of the Concept GLB. About the only thing we're still waiting on here is the latest GLE Coupe, although that can't be too far off.

Er... I hate to break it to you, but you've missed an SUV out, haven't you?

Not at all, we've just finally got to the nub of the matter (or, more accurately, this news piece). Having begun life as a GL in 2006, Mercedes' largest SUV became the GLS midway through the Mk2's life-cycle. Now we've got an all-new Mk3. And you can forget about the Concept GLB and GLE with its optional third row, because this is the seven-seat SUV daddy.

Oh yeah, I bet; the rear seats in this thing won't be any good for anything but tiny kids, eh?

Sound the 'WrongwrongWRONG!' klaxon, please. The GLS Mk3's rear-most two pews can purportedly accommodate people who are 1.94m tall. So unless you have some properly freakish eight-year-olds who stand at 6ft 4in, this should suit you fine.

What?! One metre 94cm?! That's incredible!

It is, but it has come about because - somehow - the absolutely mahoosive GLS Mk2 has become absolutelier mahoosiver for the Mk3 outing. Fully 60mm has been grafted into the wheelbase of the GLS, with a goliath 3,135mm between the axles. This is in a body which is 77mm longer than the old model (at 5,207mm overall) and 22mm wider (1,956mm overall). Fold all of the back five seats inside down - a simple enough job to do, as there's a button in the boot that will do this electrically for you - and a cave measuring 2,400 litres presents itself in the back of the Merc. You can even make its backside squat by 50mm if you want to, in order to aid with loading bulky items.

Presumably, it's not just capacious inside, but luxurious too?

Oh, most assuredly. You're looking at an S-Class on stilts here, after all. Up front, there's the gorgeous MBUX human-machine interface (HMI) for the infotainment, which is presented in its most advanced display yet, teamed to the Widescreen Cockpit of twin 12.3-inch TFT screens. Above this, for the driver, sits a high-res head-up display which sets new standards in the industry, according to Mercedes. Going back to MBUX for a moment, it can be augmented with MBUX Rear Seat Entertainment, bringing in 11.6-inch touchscreens for movies, music and internet browsing for people not sitting in the front two seats. A Rear Comfort Package Plus sees a tablet introduced into the mix, from which passengers can control any of the car's comfort and entertainment functions. All seats are electrically adjustable and operated, while there's even seat heating and USB sockets in row three, never mind the second row. Easy Entry allows easier access to the rear-most pair of pews, the middle-seat occupants have up to 87mm more legroom than they did before (as the centre row of chairs can slide backwards and forwards), and there's FIVE-zone climate control on the options menu. Don't need seven seats in your GLS? Then go for the six-chair option, which replaces the centre three-strong bench with a couple of luxurious individual seats. This is something BMW will offer you in the comparable X7, of course, but it's the first time it has appeared in the GLS.

Right, so what about the outside?

The GLS is designed along the tenet of 'Sensual Purity'. Which is supposed to mean no sharp edges and chamfers to the bodywork, although we think it could just as easily mean 'it looks a lot like a larger GLC or GLE'. Nevertheless, it's a handsome thing and, in the pictures, the aesthetics seem to disguise its obviously bulky frame well. All models will have 112-LED Multibeam headlights as standard, which can beam one lux of light down the road to a distance of 650 metres when they're on 'mains'. Chrome under guards front and rear, an octagonal-shaped radiator grille and power dome strakes on the bonnet complete the GLS' new look, although it's not just trying to be pretty for the sake of it - it's also more aerodynamically efficient than the old model, with a co-efficient of drag rated at 0.32 instead of 0.35. This not only makes it easier on fuel, it should also bolster its refinement qualities too.

Talking of fuel, what engines have we got in the new GLS?

Two diesels to kick us off. Both are the OM656 2.9-litre inline-six turbodiesel, so choose from either the 286hp/600Nm iteration in the GLS 350 d 4Matic or the stronger 330hp/700Nm unit found in the GLS 400 d 4Matic. Doesn't matter which of these diesels you pick, you should see around 37.2mpg (NEDC-correlated) with CO₂ emissions of circa 200g/km. Petrol GLS models will all be augmented by the EQ Boost 48-volt system, which also ensures that the biggest Mercedes SUV has the E-Active Body Control active suspension. A six-cylinder GLS 450 4Matic, with 367hp and 500Nm, will be offered but not in the EU, so we need to focus on the GLS 580 4Matic, which will arrive with us soon after the GLS' launch in Q3 2019. This has a 489hp/700Nm V8 motor that is bolstered by the EQ Boost's additional 22hp/250Nm. All told, the GLS 580 should be capable of 28.8mpg with 224g/km of CO₂, but we don't know anything yet about performance. What we do know, and what you might have picked up from the constant '4Matic' references, is that all GLS models will be four-wheel drive, while they will also use the 9G-Tronic nine-speed automatic gearbox and enhanced Airmatic air suspension with the Adaptive Damping System Plus fitted. A load of driver-assist safety systems will be available, as will a Carwash function which automatically preps the car for entering an automated carwash. Although we suspect GLS owners have a valet to clean their car for them...

Where will the GLS be built?

At Mercedes' Tuscaloosa plant in Alabama, USA. The GLS was primarily launched (as the GL) 13 years ago to capitalise on 'soccer moms' in the US, which is its main market, so it made sense to reveal the American-built SUV at none other than the New York Auto Show.

Matt Robinson - 17 Apr 2019