Heading into the 2017 Formula One season Lewis Hamilton and Sebastian Vettel were the sport's leading racers, having claimed six of the last seven titles between them. And yet, despite F1's history of fractious relationships, this pair remained friendly rivals.
But, with a rush of blood to Vettel's head, that relationship has become combustible to say the least and Britain is set to get a front-row seat in less than three weeks' time when the Formula One roadshow arrives at Silverstone.
It was on the 19th lap of the eighth race of the season in Azerbaijan that the pair's long-standing rivalry took a sharp turn for the worse.
After a relatively calm opening dozen circuits the safety car was called out three times in 10 laps in what became a concertinaed and somewhat chaotic grand prix.
During one of these enforced periods of compression, with Hamilton at the front, Vettel drove into the back of the British driver's Mercedes.
The German was infuriated, believing that Hamilton had deliberately slowed down. His extraordinary reaction was to pull alongside Hamilton's car and veer into it.
The first collision was of questionable causation. The second bump looked obvious and deliberate. The punishment was a curiously minimal 10-second stop-and-go penalty and three more points added to his license.
During the race, Vettel's reaction could be heard over the team radio: "He brake-tested me. What the f**k is going on?"
But any driver on any surface in any type of car knows that when you drive into the back of another vehicle the blame is yours, no matter how you feel the car in front behaved. Even if Hamilton was making life difficult for Vettel, it was the German driver's responsibility to make sure no such collision occurred. That he pulled alongside his rival and swerved into his car was extraordinary to say the least.
"A 10-second penalty is not enough for driver behaviour like that," said Hamilton.
To add insult to injury, Vettel finished the race one spot ahead of Hamilton in fourth place after the latter was forced to pit again to fix a loose headrest.
It is almost a footnote that Red Bull's Daniel Ricciardo won his first race of the season ahead of Valtteri Bottas, with 18-year-old Lance Stroll claiming third and a place in the record books as the youngest driver ever to step on the podium.
Vettel and Hamilton remain one and two in the 2017 Driver Standings, having won three races apiece thus far this season. And it could well be this that lights the touch-paper for the intensification – and deterioration – of their relationship.
Despite winning seven of the ten championships in which they have both competed (four for Vettel and three for Hamilton), the pair have never finished one-two at the end of the season. While the duo are this era's dominant drivers – between them they have won 101 of the 196 races since starting in 2007 – they have never before had machinery which was so evenly matched.
This season that has changed. After Vettel claimed the first victory of the season in Melbourne, Hamilton declared: "It's been a privilege to be racing in an era with him and now finally at a period of time when we can actually have a real race."
The 32-year-old added: "This year you are seeing the best against the best with the best drivers at the top." This could also perhaps have been seen as a snarky aside against Hamilton's former colleague, the now-retired Nico Rosberg, who won last year's championship.
This season is the first for many years that Ferrari have produced a car which is capable of properly challenging for a title. After Sunday's race in Baku the words coming from the two drivers were much less complimentary.
Vettel certainly wasn't planning on accepting the blame, while a furious Hamilton claimed that his rival had "disgraced himself".
Mercedes' non-executive chairman, Niki Lauda, himself half of one of the sport's greatest rivalries with James Hunt, said: "He [Vettel] freaked out in himself. Lewis will hit him one day. Not with the car but with the fist. If I was Lewis, I would speak to Sebastian and ask him what is wrong.
"Sebastian said he didn't do anything wrong. This is his normal reaction. He is still somewhere else in his brain. After three days hopefully he realises. When you hit somebody up the a**e it is your fault. No question. But to drive next to him and hit him on purpose, I have never seen anything like this."
The spectacle of the two best drivers of their generation racing head-to-head is exactly what Formula One needed after the tedium of Mercedes' domination, which was preceded by Red Bull's.
It is possible that away from the heat of the moment the pair will reconcile, but with the Austrian Grand Prix in two weeks followed swiftly by the British GP, and with the title race set to go all the way to the wire, there are plenty more opportunities for this rivalry to stay ugly.