Former world champion Kimi Raikkonen will leave Ferrari at the end of this season and rejoin Sauber.
The 38-year-old Finn will be replaced at Ferrari by 20-year-old Monaco-born Sauber driver Charles Leclerc, who will partner Sebastian Vettel in 2019.
Raikkonen has spent five years at Ferrari in his second spell at the Italian team.
He has signed a two-year contract with Sauber, where he made his Formula 1 debut in 2001.
"Feels extremely good to go back where it all began," said Raikkonen in a post on Instagram.
Raikkonen is the last Ferrari driver to win the world championship in 2007, before taking a two-year break from F1 in 2010 to compete in the World Rally Championship.
He returned to the sport with Lotus in 2012 and then rejoined Ferrari in 2014. He has 20 grands prix wins and 100 podiums in his career to date.
"Signing Raikkonen as our driver represents an important pillar of our project, and brings us closer to our target of making significant progress as a team in the near future," said Sauber team boss Frederic Vasseur.
Ferrari team principal Maurizio Arrivabene said: "Kimi's contribution to the team, both as a driver and on account of his human qualities, has been fundamental. He played a decisive role in the team's growth and was, at the same time, always a great team player."
'Dreams do come true'
Leclerc is a member of the Ferrari Driver Academy
Leclerc has been picked as the Ferrari's next potential star, after impressing in his debut F1 season.
"Dreams do come true," Leclerc, a member of the Ferrari driver academy, posted on Twitter. "I will be eternally grateful to Ferrari for the opportunity given."
In a statement he paid tribute to his late father and his friend and godfather Jules Bianchi, another Ferrari protégé, who died in 2015, nine months after a crash at the 2014 Japanese Grand Prix.
"To a person that is not part of this world anymore but to whom I owe everything of what is happening to me, Papa," said Leclerc. "To Jules, thank you for all the things you learnt me, we will never forget you, and to all the persons that supported me and believed in me.
"I will work harder than ever to not disappoint you. But first, there is a season to finish with an amazing team that gave me the opportunity to fight and show my potential."
Why is Raikkonen leaving?
Raikkonen's move has come despite an online campaign from fans aimed at persuading Ferrari to keep him on for another season. As of Tuesday, nearly 90,000 fans had indicated their desire for the veteran to be retained.
He remains one of the most popular drivers on the grid, many fans finding his notoriously taciturn and no-nonsense manner in public appealing.
Raikkonen won the drivers' championship in 2007
This is despite him failing to win a race in his five years since returning to Ferrari in 2014, and being out-performed by team-mates Fernando Alonso and then Vettel.
Keeping Raikkonen had been Vettel's preferred option, too, but in the end Ferrari have stuck with a decision made by their late president Sergio Marchionne, who made the call back in June to promote Leclerc.
Marchionne died unexpectedly in July and has been replaced at Ferrari by chairman John Elkann, a scion of the Agnelli family that has long controlled Fiat and its affiliated companies, and chief executive officer Louis Carey Camilleri.
Both were at the Italian Grand Prix, where Elkann broke the news to Raikkonen before the race that he may not be retained, according to sources close to the team.
He then failed to win the race despite starting from pole position, and by defending against Vettel on the opening lap arguably contributed to the chain of events that led to Vettel spinning to the back after colliding with Lewis Hamilton, who went on to win the race.
It was the latest in a series of events this year in which Ferrari and/or Vettel have cost themselves points against Hamilton.
Marchionne made the original call to promote Leclerc after his impressive start to his debut season this year.
After three shaky races, Leclerc turned a corner at the fourth event in Baku, where he took the unfenced Sauber to a remarkable sixth place.
His strong form has continued and after 14 races he has out-qualified team-mate Marcus Ericsson 11 times at an average advantage of just over 0.5 seconds.
A number of drivers - including Vettel, Hamilton and two-time champion Fernando Alonso - have praised Leclerc and said he has a bright future.
A member of the Ferrari driver academy, Leclerc was given a grand prix debut with Sauber after his championship-winning season in the Formula Two feeder series last year with the intention of moving him to Ferrari in 2019 if he performed to expectations.
Why not Raikkonen?
At the same time, Raikkonen, whose last victory was at the 2013 Australian Grand Prix for Lotus, has not made a compelling case to be retained.
His form in 2018 has been much the same as in the previous four years.
Generally a little off Vettel's pace in qualifying, Raikkonen has had varied performances in races, mixing occasional strong drives with others in which he lacks pace. He has also failed to make up a place on the first lap since the final race of the 2016 season, and has made a habit of under-performing in qualifying because of mistakes at high-pressure moments.
Raikkonen is the last driver to win the title for the team, in 2007, but had been paid off by Ferrari at the end of 2009, one year short of the end of his contract, to make way for Alonso, after unconvincing performances.
Raikkonen was re-signed for 2014 because Ferrari feared the Spaniard was becoming disillusioned with the team because of their inability provide him with a competitive car - he had nearly won the title in 2010 and 2012, but each time was fighting a faster Red Bull.
Alonso duly left at the end of 2014, having put in performances of an entirely different level to Raikkonen that year, and was replaced by Vettel.
Vettel has also out-performed Raikkonen, if not quite to the same level as Alonso, and the Finn has fallen into a de facto support role, even if Ferrari never quite made that completely clear.
Part of the background to the decision is Ferrari's uncertainty as to whether Vettel is always performing at the top of his game - some in the team have privately questioned whether, on the occasions Raikkonen has been ahead, this is whether Vettel's level has dropped rather than his team-mate's risen.
-- Courtesy of BBC Sport