Alonso won his world titles with the team in 2005 and 2005.

The Spaniard, also a two-time Le Mans 24 Hours winner who turns 39 this month, had raced most recently for McLaren in the 2018 season.

Alonso replaces Australia's Daniel Ricciardo, who is moving to McLaren at the end of the year. Ricciardo is taking over from Carlos Sainz ahead of his switch to Ferrari.

"Renault is my family, my fondest memories in Formula One with my two World Championship titles, but I'm now looking ahead," Alonso told Renault's website.

"It's a great source of pride and with an immense emotion I'm returning to the team that gave me my chance at the start of my career and which now gives me the opportunity to return to the highest level.

"I have principles and ambitions in line with the team's project. Their progress this winter gives credibility to the objectives ... and I will share all my racing experience with everyone from the engineers to the mechanics and my teammates.

"The team wants and has the means to get back on the podium, as do I."

Alonso has competed in 311 grands prix, winning 32 of them. He starred for Renault in the early years, before quitting McLaren after one season after a turbulent campaign alongside the then-rookie Lewis Hamilton.

He returned to Renault before a four-year period at Ferrari where he came close to winning the title twice. After falling out with the Italian team, he went back to McLaren, but the switch proved unsuccessful.

Alonso quit the sport after four seasons with McLaren, setting his sights on becoming only the second driver since Britain's Graham Hill to complete the so-called Triple Crown - winning the Monaco Grand Prix, Le Mans 24 Hours and Indy 500.

Despite winning the famous sportscar endurance race in 2018 and 2019, he has not been able to crack the Indy 500, despite a remarkable effort on his first appearance in 2017.

PA

Australian Associated Press