Lauda, who died earlier this week at the age of 70, had a lung transplant in the summer of 2018. He said at the end of last year that the handwritten note he received from Vettel while in hospital was a “great pleasure”.

Asked in the build-up to the Monaco Grand Prix about writing that letter, following Lauda’s passing, Vettel said “respect says it all”.

“I heard he was not doing well and not doing well for a while, and he wasn’t in the mood to pick up the phone or the state to talk over the phone,” said Vettel. “You think what would you appreciate if you were in that situation? Just reading a little note is a nice thing. 

“For me it was a no-brainer and a sign of respect.”

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Vettel, an enthusiast of F1 history, called it a “privilege” to have spent time with Lauda, who was a key figure for Ferrari. He said he had taken the opportunity “to ask him all sorts of things: how the cars were, how the time was with Ferrari, how was Enzo Ferrari”.

Vettel said that his respect was based on “what he’s achieved, the person he is, what he’s done for the sport”. 

“I feel privileged I had the chance to not just know him, but chat with him regularly, enjoy jokes with him and so on,” added Vettel. “His sense of humour was very straight. Sometimes you couldn’t tell if it was just a joke or just a statement. I certainly enjoyed that. 

“You don’t come across people like him very often, not just in F1 but in general. He was a unique person.”

Niki Lauda, Ferrari 312T

Lauda went on to become non-executive chairman of the rival Mercedes team but Vettel said he was always a “gentleman”.

He joked that Lauda had such an “honest tongue” that “I think sometimes people were not thinking he was telling the truth when he was”. 

Asked what Lauda was like compared to what people who only saw him on TV would have known, Vettel said: “He was just like that. There’s a lot of people that are not the way you see them on television. They are growing in numbers, quickly! 

“But Niki wasn’t one of them. He was who he was. He never pretended to be anything or anybody else. He was very outspoken, a true character, a true racer, passionate for the sport – a lot of things people respected. 

“He’s leaving a big gap that we won’t be able to fill.”