And Rosberg said as recently as last week that Hamilton, the winner of the last four grands prix on the trot, is still welcome to knock on his Monaco apartment and ask for a quick hamburger.
But as Hamilton sniffs his first title since 2008, the Briton is starting to take his boxing gloves off.
In an interview in Monaco, he claimed he is "hungrier" than Rosberg due to their respective upbringings: the German with his "jets and hotels and boats", and Hamilton who slept "on a couch" in a "not-great place" in suburban UK.
Many might draw quick parallels between Hamilton and Rosberg at Mercedes in 2014 and Ayrton Senna versus Alain Prost, and their utter domination at McLaren in 1988.
Like Senna, Hamilton might be seen as the more feisty and aggressive, while like Prost, Rosberg is the calculating thinker.
Hamilton smiled when told of the comparison.
"I think the fight between them (Senna and Prost) was more livery than what is happening with us right now," he is quoted by Brazil's Totalrace.
"In our case, it's all wonderful," Hamilton laughed.
However, Hamilton indicated he is in fact open to a more "lively" competition with Rosberg, admitting even that a Suzuka 1988-style showdown would be "cool".
At Suzuka in 1988, the Senna-Prost rivalry reached its infamous zenith when the pair collided at the chicane.
"Not that I'll take him out," Hamilton smiled, "but it was pretty cool when it reached a climax between them at Suzuka.
"I think things will get more livery as the year goes on and I hope we can look back in a few years' time and say that we had something like that."