Friends from their teens right through to when they entered F1 - remember their little dance in Melbourne 2008 when Rosberg first joined Hamilton on the F1 podium - all that came to an end once they were partnered at Mercedes in 2013.
It started well enough, but then slowly it began to deteriorate as each used every trick in the book - and then some - in a bid to gain superiority. By the end it was acrimonious, to put it mildly, with Hamilton barely able to utter the German's name.
Speaking on his own You Tube channel, Rosberg has advised the likes of Vettel and Verstappen to make hay while the sun shines, warning that his former friend and teammate is merely going through a difficult phase from which he will return guns blazing.
"Lewis, for him, he was really struggling", says the German, reflecting on China. "He was struggling all weekend and doesn't really understand, looking at his interviews.
"It's a typical phase for Lewis when it doesn't go perfectly and he starts to lose that edge a little bit, lose a touch of motivation and then he just struggles for a while.
"Usually he struggles for one, two or three races, and those are the races when as his opponent in the championship you have to maximise, and Sebastian failed to do that," he adds, referring to Shanghai.
"That's a big setback for him as well because Lewis always come back and when he comes back he comes back so damn strong that he's almost unbeatable. Let's see when that happens."
The German, who retired just days after finally winning the title in 2016, had some advice for Max Verstappen also.
"He's one of the big talents out there and has a great future but driving the way he is at the moment he's not going to be able to be world champion.
"Five mistakes in three races, and five major mistakes, it's too much," he added. "(China) was one of those extremely hard days for a young driver where you take the championship leader out, take yourself out, you get a penalty, you are 100 percent at fault and your teammate wins the race in an unbelievably awesome way. That is a hard day, that's painful. Those are the days when a young driver like Max, hopefully for him, will learn and adapt."