Just five minutes after Lewis Hamilton told Toto Wolff he would leave for Ferrari at the end of 2024, the Mercedes team boss had decided on the seven-time champion's replacement.
When Hamilton delivered the news to Wolff in late January, Fernando Alonso and Carlos Sainz were among the many drivers available for 2025, but Wolff saw the team's future with a teenager just two seasons out of go-karts, who, at that time, had never driven a Formula One car.
The only thing that had the potential to change Wolff's mind was if Max Verstappen could be coaxed away from Red Bull, but with the reigning champion contracted until 2028 it was always a long shot. Otherwise, Andrea Kimi Antonelli would be accelerated through Mercedes' junior driver programme and into the cockpit of a Mercedes to partner George Russell in 2025.
"I made up my mind five minutes after Lewis Hamilton told me he was going to Ferrari," Wolff said on Saturday following confirmation of Antonelli's promotion.
"Obviously we were discussing with other options, and obviously the Max idea couldn't be discounted completely looking at what happened at Red Bull, but instinctively this is the line-up that I always wanted."
Antonelli was scouted by Mercedes' driver development in April 2019 while he was still racing go-karts. In the years that followed, it became clear that he was an exceptional talent, exceeding expectations every time he took a step up the motorsport ladder.
Above all, his exceptional pace was the differentiator. Having turned 18 just a week ago, it's clear Antonelli still has a lot to learn -- his accident during his Friday practice debut at Monza being very public proof -- but Mercedes is convinced any short-term pain will be rewarded in the long term.
"I think one of the key ingredients of the really best ones is to hit the ground up and running, and go straight, fast," Wolff said. "I've spoken about the F3 test in Silverstone in the rain with some F2 drivers, where on his first flying lap, he was four seconds quicker than the rest. And that bit him yesterday [in the practice session].
"That's going to be a valuable lesson, because it's not about having fun in an F3 car in Silverstone in the rain, this is Formula One, there is a lot of responsibility that comes with it.
"And that's why Kimi yesterday learned in a very, very hard way. I think that moment must have been very tough, but sometimes, it needs to sting, then it sticks."
Preparing Antonelli for F1 in such a short space of time has been a significant undertaking. After winning the Formula Regional European Championship (essentially Formula 4) in 2023, Antonelli skipped the next logical step to Formula 3 this year and was promoted straight to Formula 2. He is seventh in the standings with two race victories, but has been dovetailing his F2 campaign with private F1 tests with Mercedes.
The last comparable step from feeder series to front-running F1 team was Hamilton's jump from GP2 in 2006 to McLaren race seat in 2007, although back then the sport's regulations allowed for far more testing to get up to speed. Under today's F1's testing restrictions, running in a current car is limited to occasional tyre tests, meaning Antonelli's first experiences in F1 machinery have been in Mercedes' 2021 and 2022 cars (known in F1 as TPC -- testing of previous car) in Austria, Imola, Silverstone, Barcelona and at Spa-Francorchamps this year.
There was speculation earlier this year that Antonelli could be loaned out to Williams when it first became apparent that the Mercedes-powered team was considering axing Logan Sargeant during the season, a decision it followed through with this weekend in Italy. However, Wolff believes the private tests, combined with Friday practice appearances (including the one that ended with a crash on Friday at Monza and a second lined up for Mexico), was the best way forward.
"When you look at the blueprint [for arriving in F1 as a rookie] back in the day that Lewis gave, it was a lot of testing to prepare not only for the driving, but also going through the race weekend preparation," Wolff said. "So that TPC program [with Antonelli] is going to continue.
"When thinking about an opportunity at Williams, we opted to continue with our program and continuing to educate Kimi, finishing with another FP1 session
"And then doing Abu Dhabi [post-season test], and taking it from there. Because I think the more kilometers you do, especially in a car that is not great [Mercedes' 2022 car], the TPC car was not our best car.
"It's going to get him between 15 and 20 days under his belt, and that's important."
Speaking earlier this year, Antonelli admitted he wasn't sure if he was ready for F1, but the private testing has helped build his confidence.
"Well between that period of time and now, I've been doing some TPCs, and I've seen some major improvements and I've been feeling much better in the car," Antonelli said. "I have to say, one of my weakest points I would say is the long run, and in the last few TPCs, I've been improving that a lot.
"Also because I was feeling much better with the car, also with all the procedures, made me change the mind. Of course, I still have so much to learn, learning how to deal with a full race weekend, and I think yesterday was the proof!
"And learning with all the, managing all the procedures, not only on the steering wheel but also starts. So still so much to learn, but every time I got in the car, I feel so much better."
That experience will be crucial, especially if Mercedes' impressive development trajectory from the last few months continues into 2025 and the team is a genuine title competitor.
There is no doubt that Hamilton's presence at the team will be greatly missed -- from a pure driving, experience, and a marketing point of view -- but Wolff said there was never a possibility of finding a like-for-like replacement.
"When Lewis decided to go for another challenge, no one can replace him in all of his, let's say, stature," Wolff said. "But that doesn't mean that the team is not going to prosper with two drivers that represent the future.
"I'm sure that if we are capable of giving George and Kimi a car that can win races and championships we can hopefully continue the legacy of championship titles that Lewis left here, with these two, as Mercedes."