Lewis Hamilton has said watching his Mercedes successor Kimi Antonelli win his first world championship was the "highlight" of his Formula 1 season.
Antonelli, who replaced the seven-time world champion at Mercedes at the start of 2025 following his move to Ferrari, clinched the title at Sunday's Mexico City Grand Prix, becoming the youngest champion in F1 history at just 20 years old.
Hamilton, along with fellow multiple title-winner Max Verstappen, celebrated Antonelli's achievement on the podium and praised the Italian in a post on social media on Monday.
"Let me start with a huge congratulations to the new champion, Kimi Antonelli," Hamilton, 41, wrote on Instagram. "To have seen your journey so closely and to be there celebrating with you, was a highlight of my year. So well deserved and a record that will stand for a long time.
"It was great to see your team at Mercedes celebrating with you. Enjoy this moment, keep your family close, keep your passion and your energy."
Antonelli was just 18 when he stepped into Hamilton's seat at Mercedes, facing the daunting task of replacing the most successful driver in F1 history, who won six of his seven world titles with the Silver Arrows.
But the Italian has enjoyed a remarkable second season, beating teammate George Russell and Ferrari's Hamilton -- among others -- to the championship with four rounds still scheduled to take place.
Hamilton's congratulations came alongside an admission of frustration over Ferrari's weekend in Mexico, where he felt the team had missed an opportunity to win and also appeared to acknowledge tensions following Charles Leclerc's actions on the opening laps.
"Our own weekend was one full of challenges," Hamilton said. "We had a lot thrown at us but our mechanics and engineers did an incredible job.
"We've grown so much together this year, and that progress has taken a huge effort from everyone on the track and back at the factory. That's why losing what could've been a win hurts so much.
"We need to grasp every opportunity we have, so it's incredibly frustrating, and I can't pretend otherwise."
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He added: "Battling is necessary, but when that battle costs the team, we have to be honest about it and learn from it.
"We can push each other to the limit and still honour the responsibility to everyone who put us on that track."
Despite his frustrations, Hamilton insisted his commitment to Ferrari remained unchanged.
"I'll keep giving everything I have. My belief in this team hasn't changed and neither has my responsibility to help us get this right," he said.
"Stick with us. I'm only just getting started with this team, and we have so much more to come."