Seven-time world champion Lewis will join the Scuderia next year after deciding to activate a one-year break clause in his Mercedes contract.
It will be Hamilton’s third F1 team, having debuted in the sport with McLaren before moving to Mercedes in 2013 – where he has won six world titles in 11 years at the Silver Arrows.
And his half-brother Nicolas, a driver in the British Touring Car Championship (BTCC) and a public speaker, explained how Lewis told him about the stunning news, admitting he was shocked.
“Yeah, it was so surprising,” he said in an Instagram live video.
“I do public speaking, so I was doing a public speech for Coca-Cola and Lewis called me the night before and I was at dinner so I said ‘Hey bro, I’ll call you back when I can.’
“Then I called him later at night and he didn’t pick up and then he told me he was in bed. Then he said ‘are you around?’ I said ‘I’m just heading into work, I’ve got a speech to do and I’ll catch you later tonight because I’ll be free.’
“He said ‘I could really do with speaking to you now, are you in a place where you can talk but can you talk without anyone hearing?’
“I said ‘yeah’ and then he said ‘so I’m going to Ferrari in 2025.’ I was like ‘What! Are you joking? That’s crazy!”
Hamilton will now embark on a final season farewell with Mercedes, starting with the Bahrain Grand Prix on 29 February – 2 March.
In an emotional social media post on Saturday, he said: “Mercedes has been a huge part of my life since I was 13 years old, so this decision has been the hardest I’ve ever had to make.
“I’m incredibly proud of all that we’ve achieved together and I’m very grateful for the hard work and dedication of everyone I have worked with over the years and of course Toto, for his friendship, guidance and leadership.
“But the time is right to make a change and take on a new challenge. I still remember the feeling of taking a leap of faith into the unknown when I first joined Mercedes in 2013. I know some people didn’t understand it at the time but I was right to make the move then and it’s the feeling I have again now. I’m excited to see what I can bring to this new opportunity and what we can do together.
“I feel incredibly fortunate, after achieving things with Mercedes that I could only have dreamed of as a kid, that I now have the chance to fulfil another childhood dream. Driving in Ferrari red.”
The 39-year-old is set to appear at Mercedes’ 2024 car launch next Wednesday, 14 February, at Silverstone.