Australian driver Daniel Ricciardo is leaving Red Bull at the end of the season and joining Renault, the two Formula One teams announced on Friday.
"Daniel Ricciardo has advised us that he is to leave the team at the end of the 2018 season," Red Bull posted on their website.
Renault followed a little later by tweeting: "We are delighted to announce that @danielricciardo will join @RenaultSportF1 as race driver from 2019."
Ricciardo is fifth in the 2018 drivers' standings and has won in China and Monaco this season.
Renault supplies engines to Red Bull but have not won a race since fully rejoining Formula One three years ago.
Their best-placed driver is Nico Hulkenberg in seventh, while 23-year-old Spaniard Carlos Sainz is 11th.
"It was probably one of the most difficult decisions to take in my career so far," Ricciardo told the Renault website. "But I thought that it was time for me to take on a fresh and new challenge."
Renault released a statement that appeared to confirm that Sainz would be making way for Ricciardo.
"Renault Sport Formula One team is happy to confirm the arrival of Daniel Ricciardo to join Nico Hulkenberg as a driver starting from next season," Renault said.
Ricciardo's switch to a team outside the big three represents a gamble. While Renault are one place behind Red Bull in the constructors' standings, they have only 82 points while third-place Red Bull have 223.
"I realise that there is a lot ahead in order to allow Renault to reach their target of competing at the highest level," he said.
"But I have been impressed by their progression in only two years, and I know that each time Renault has been in the sport they eventually won. I hope to be able to help them in this journey and contribute on and off track."
Renault team president Jerome Stoll said the signing underlined their ambition: "Renault decided to come back to Formula One to fight for World Championships."
- Dominos tumbling -
While the leading team, Mercedes, announced before the German Grand Prix on July 22 that they had locked their two drivers, Lewis Hamilton and Valtteri Bottas, to contract extensions, Ricciardo's switch could start dominos tumbling elsewhere in the paddock.
The promising Sainz, who like Ricciardo is a product of Red Bull's driver development programme, is one driver already looking for a seat.
Red Bull meanwhile need to find a replacement for Ricciardo.
"We will now continue to evaluate the numerous options available to us before deciding on which driver partners Max Verstappen for the 2019 season," team principal Christian Horner told the Red Bull website.
Ricciardo drove for Red Bull's junior Formula One team Toro Rosso in 2012 and 2013, recording a best finish of 14th. He switched to the flagship Red Bull team in 2013 and has since won seven races and recorded 29 podium finishes. He finished third in the drivers' standings in 2014 and 2016.
"We fully respect Daniel's decision to leave," Horner said. "We wish him all the best in his future."
Daniel Ricciardo, who won in Monaco with Red Bull in May, has decided to switch to Renault for next season.