Valtteri Bottas has returned to Mercedes as the team's F1 reserve driver in 2025.
Sauber dropped the Finnish driver at the end of the 2024 season after three years together but Bottas will rejoin the Silver Arrows - where he raced from 2017-2021 and claimed five constructors' titles in a row - as backup to George Russell and Kimi Antonelli next year.
A spot has opened up as a reserve at Mercedes after Mick Schumacher left the team following the 2024 season finale in Abu Dhabi.
Bottas, 35, said: "I'm happy to finally answer the question I've posed over the past month. Returning home to the Mercedes family as third driver for 2025 is what's next and I couldn't be more pleased.
"I want to thank Toto, the team at Brackley, and everyone at the three-pointed star for welcoming me back with open arms.
"Despite the challenges of the past few years, I know that I've still got so much more to contribute to F1.
"Since I was a five-year-old kid growing up in Nastola, Finland, my focus has been on achieving success in the top tier of motorsport. I've been fortunate to have enjoyed many incredible moments in my 12 years of racing in F1 so far.
"As I return to the place where so many of those moments were achieved, I'm looking forward to using all the knowledge I've gained to help the team to perform and progress towards our goal of fighting for world championships."
Mercedes boss Toto Wolff added: "Welcome home, Valtteri! It's great to have you back. His impact and contribution in the five years he was with us previously as our race driver was immense.
"Along with scoring multiple Grands Prix wins, he played a vital role in five of our championship victories. His technical feedback and input were important in helping us to those successes and pushing the team forward. Not only that, but he was also a fantastic colleague and team member.
"His dry sense of humour and personable nature made him a firm favourite with everyone at Brackley and Brixworth.
"In his role as Reserve Driver, all those qualities will be incredibly important in helping us compete for world championships and supporting both George and Kimi on track."