The Austrian disregarded Horner's pledge of confidentiality and relayed the development to the outgoing Coulthard just as rising star Sebastian Vettel was poised to commence his Red Bull era.

An extract from Horner's forthcoming memoir, Drive, which launches on October 22, stated: "There was a month to go until Silverstone, so I had little option but to mention the suggested plan to Helmut.

"Having told him the situation, I then stressed the importance of DC [Coulthard] making any announcement himself. 'This has to come from DC,' I said. 'Please don't breathe a word.'

"The next morning before practice, DC went to the toilet and stood at a urinal next to Helmut."

Horner went on to recall how Coulthard immediately stormed to the garage in order to verify the speculation with him. And he could tell from Coulthard's demeanour that "'I hear you're retiring at Silverstone then,' Helmut said, smiling. DC was stunned. 'How do you know that?'

Horner went on to recount how Coulthard immediately made his way to the garage to confirm whether the rumour was true. He could tell straight away from Coulthard's body language that "something was wrong."

"'I think I've just been retired in a toilet," he said, looking despondent. "I was annoyed. I'd wanted DC to know he was respected by everyone at Red Bull and that his departure was being handled with sensitivity.

"Typically, Helmut had come in like a wrecking ball and crushed a delicate process. 'Look, David, this needs to be your choice,' I said. 'And it needs to be your announcement. But you can see how things are playing out with Sebastian."

At the time, Vettel was widely regarded as the next great talent in F1, having impressed across several seasons at Red Bull's former sister team, Toro Rosso.

Ultimately, it proved the correct choice, as Vettel secured second place in his maiden Red Bull campaign before claiming four consecutive championships.

Coulthard has subsequently flourished as a broadcaster and remains a Sky Sports fixture, while Horner's two-decade tenure at Red Bull has concluded as he considers a possible F1 comeback.