Almost as soon as the 1989 San Marino Grand Prix had ended, a crack appeared in McLaren's red-and-white armoury. Alain Prost collected his trophy and walked out, brushing aside the official press conference (which would later attract a $5,000 fine) without pausing to speak to the French media.
In the absence of any comment from the team, journalists were left to draw their own conclusions from what they had seen on the racetrack. Ayrton Senna had taken the lead from the start and pulled out 2.7 seconds on Prost in the first three laps. At the start of lap four, Gerhard Berger had smashed into the same wall Senna would hit fatally at Tamburello corner five years later, the Ferrari quickly engulfed in flames.
Such an unexpected sight - and the initial thought that the driver was trapped in the cockpit - prompted the red flag. Berger survived with nothing more than light burns to his hands. The same could not be said for a smouldering relationship that was about to burst into metaphorical flames.
Prost had no interest in celebrating a McLaren one-two with Senna © LAT
It later transpired that Senna, anxious to avoid the sort of first corner collision that had cost him dearly in Brazil, had suggested it would be foolish for the McLaren drivers to race each other.
He had proposed that whoever made the best start should remain unchallenged into and through Tosa, the corner at the end of the long straight. Prost had duly abided by the agreement.
Assuming the deal would be the same at the restart, Prost made the better getaway and led through Tamburello and on towards Tosa. That seemed to be that. Except that Ayrton had other ideas and rushed into the space Prost, in his innocence, had left available as he took the normal racing line into Tosa. Senna assumed the lead and, with it, any hope of the McLaren drivers ever working together again.
ALAIN PROST: "I saw him on the left and there was plenty of space and I thought, it's OK, I'll take the normal line to make a better exit - and he overtook me."
Word of the agreement filtered out during the next few days. By the time the teams had gathered at Monaco less than two weeks later, talk of a damaging split within McLaren was high on the media agenda. Sensing trouble, Ron Dennis called a press conference and explained that he had known nothing about the private agreement between his drivers.
He said Ayrton had been forced to apologise to Alain, all was well with the world and it would be nice if the media would stop writing stories to the contrary. Dennis's optimism had been based on a head-to-head discussion with his drivers at a test session at Pembrey.
Making a special trip by helicopter to the club circuit in Wales, an angry Dennis had marched Senna and Prost into the team's minibus and demanded an explanation. At the end of a tense exchange, Dennis made it clear that no driver was bigger than the team.
NEIL OATLEY: "It was unusual for Ron to turn up to a test like this without good reason, so we knew something was going on - but we had no idea what that might be. From our point of view, the test seemed normal. Although we obviously didn't realise it at the time, that was probably the last time the drivers spoke to each other."
Prost had stayed behind Senna as agreed during the first start at Imola © LAT
STEVE NICHOLS: "I was Ayrton's race engineer but knew nothing about the agreement. I had a little bit of sympathy with him and what you might call a very technical get-out clause in that this had been a restart, so all bets were off.
"On the other hand, if you make an agreement, then stick to it. Ayrton got a good run at Alain [into Tosa]. He was alongside, sitting there thinking, 'What do I do?' You know that's not in his psyche. But, if you made an agreement - then, yes, you do lift."
ALAIN PROST: "In the meeting with Ron, I did not talk. I just listened. Ron asked Ayrton if there had been an agreement and he said 'Yes', there was, but only for the first start, not for the second. But, more important, he said I had overtaken him!
"I said, 'I don't know how many million people had seen what happened on television'. He had overtaken me and this was not what we had agreed. It took maybe 20 minutes before Ayrton would accept what had happened. It was unbelievable."
JEAN-LOUIS MONCET: "In the beginning, the French journalists could see the atmosphere between Senna and Prost was very good. But then it changed at Imola. Alain asked Johnny Rives [motor sport correspondent for L'Equipe] and I to go with him on his jet to the test in Wales. On the way back, he talked to us about the deal with Senna at Imola.
"He said that Ron had been really upset and he was very, very hard with Ayrton. He had said to Ayrton, 'If you have a deal, you must respect it'. Alain told us that Senna was crying. Then Johnny wrote the story."
Dennis had finished his press briefing at Monaco by denying there was a rift within the team: 'It's not right that we should be portrayed this way,' said Dennis. 'McLaren likes to have fun while racing.' He was hard-pressed to see the funny side when L'Equipe hit the streets the morning after he had told the media all was sweetness and light.
Prost, who claimed he had been speaking off the record to Rives, was quoted as saying: 'I do not wish to drag McLaren into difficulties caused by the behaviour of Senna. McLaren has always been loyal to me. At a level of technical discussion, I shall not close the door completely but for the rest I no longer wish to have any business with him. I appreciate honesty and he is not honest.'
McLaren tried to play the feud down next time out in Monaco, but it failed © LAT
Senna, deeply upset by the story, was just as forthright with his response. 'I am persuaded that in acting like that Alain wanted to implicate me, make me carry the can, make me culpable, in a phrase: put pressure on me,' said Ayrton. 'Since that day [publication of the interview] it's finished. I don't want to hear any more talk about that guy.'
NEIL OATLEY: "From that moment, there was no conversation between the two drivers for the rest of the season. In the debrief room, there would be the two drivers, Gordon Murray and two engineers - Steve Nichols and myself. Ayrton would ask me questions about what our car was doing and Alain would ask Steve.
"Occasionally they could manage a 'Hello', but that was the limit of their communication. Apart from that, the rest of the team was immune to what was going on between the two drivers although I'm sure Ron was getting it in the ear from both of them."
DAVE RYAN: "It started out amicably enough but then it became intense rivalry. I just had to make sure we did the best we could in the garage and deal with everything absolutely fair and square. But it was pretty obvious towards the end that things were very fractious.
"We managed the garage very well. It was always one team servicing the two cars. Each car had its own crew but when one car had a lot of work on it, the other crew would come over and help and I managed to keep everything on a pretty even keel. What happened on the circuit was nothing to do with us."