The Internet is full of rumors, some which come to be true and others that do not. One such rumor is that a 4-door Mercedes AMG GT could be in the works, and in theory, would come out in 2019. Such a vehicle would be directly competing with vehicles like the Porsche Panamera, Aston Martin Rapide S and the Maserati Quattroporte.
That's the rumor. Unfortunately for those who just go a little excited, this is unlikely to happen. Mercedes currently has the CLS in its line-up. The CLS is a four-door coupe that would be a similar size to a hypothetical 4-door AMG GT. Not only is the CLS already in the line-up, we also know that there will be a brand new version of the CLS in 2018. With the CLS still in the line-up for the foreseeable future, it just wouldn't make sense to have a 4-door AMG GT because of the potential for cannibalization.
Having said all that, renders have showed up online of what a potential 4-door Mercedes AMG GT would look like. In addition to the picture at the top of the post, there are also these other two renders.