ABU DHABI • An edge of enmity has sharpened the relationship between once-close friends Lewis Hamilton and Nico Rosberg, so that theirs can now be counted among the great rivalries of Formula One.
Alongside Nigel Mansell and Nelson Piquet, Niki Lauda and James Hunt and, above all, Alain Prost and Ayrton Senna.
So, it is difficult now to remember them as the carefree, cavorting pals they once were.
Can those old pictures of them riding unicycles and sharing ice creams, playing football, table tennis and computer games be real?
When they first competed against each other, they talked about how cool it would be if they ended up as team-mates in Formula One.
Well, it is so cool now you can see a glisten on the frost.
Number of races Mercedes team-mates and championship rivals Lewis Hamilton and Nico Rosberg have each won this year. One of them will become the first to have won nine grands prix but to miss out on the driver's title.
These two 31-year-olds were first team-mates in 2000, when they were in karting.
They raced for MBM (Mercedes-Benz/McLaren) and Hamilton became European champion, with Rosberg close behind.
"They would even have races to eat pizza, always eating two at a time," recalls Robert Kubica, who raced with them then before joining them in F1.
They were unlikely friends - Rosberg, an only child born in Germany but brought up in Monaco, the son of the wealthy former F1 champion Keke, and Hamilton, born on a council estate in Stevenage - but friends nevertheless.
Hamilton would mischievously persuade the rich young Rosberg to buy him sweets.
The Briton, according to their old karting boss Dino Chiesa, wanted to play more and fight more in those days. And he was the faster driver, even then.
Rosberg, who once said that "everything relates to physics and maths", had a serious side even then. Now he speaks five languages and reads the business pages; Hamilton does not.
The pair were friends when they moved up to Formula Three, and friends still when they made it to F1 (Rosberg in 2006, Hamilton the following year).
They even got on famously when Hamilton joined Rosberg at Mercedes in 2013, but that was the beginning of the big freeze.
The two were "playing" once more in Abu Dhabi earlier this week, sparring with each other in a special press conference.
They have won nine races apiece, with Hamilton leading the pole race 12-8.
"If I was to win (the championship), it would by far be the greatest achievement of my career, for sure," he says.
And it would. But then in Hamilton's eyes he already has done.
"I feel a certain way in my heart," he said. "How I have performed. And if he (Rosberg) is labelled the world champion it doesn't necessarily mean that is the way it is in my heart."