Pop quiz: what was the best-selling flagship luxury sedan in Europe in 2017? The Mercedes-Benz S-Class? Nope. What about the BMW 7 Series? Try again. Surely not the Audi A8? Negative.

The all-electric Tesla Model S outsold all three German flagship luxury sedans on the continent last year, increasing some 30 percent to 16 132 units, according to Jato Dynamics.

The S-Class, meanwhile, managed 13 359 units (up three percent), while the 7 Series came in with 11 735 (a fall of 13 percent).

"This is an alarm for the traditional automakers such as Mercedes. It says a smaller but smarter brand such as Tesla can beat them at home," Felipe Munoz, Jato?s global analyst, told Automotive News Europe.

Munoz suggested to the publication that European automakers needed to speed up their adoption of electrification to keep up.