Britain's three-time world champion Lewis Hamilton will have a new Mercedes team-mate this year after his long-term rival Nico Rosberg shocked the sporting world by retiring from Formula One.
Mercedes have dominated grand-prix racing for the past three years and the surprise vacancy at their team quickly became the hottest ticket in the sport.
Fernando Alonso and Sebastian Vettel were both considered by Mercedes to drive alongside Hamilton but the world champions appointed Finnish driver Valtteri Bottas in January.
Here, we take a closer look at the man who could be Hamilton's closest challenger for the title this year.
What do we know about Bottas?
The 27-year-old made his grand prix debut for Williams back in 2013. He partnered Felipe Massa, the Brazilian who missed out on winning the world championship by a single point to Hamilton, for three years and comfortably out-scored and out-performed his team-mate. The Finn's impressive displays encouraged Ferrari to move for him as a replacement for Kimi Raikkonen in the summer of 2015, but Williams blocked their swoop. Bottas is yet to win, or record a pole position in F1, but has appeared on the podium on nine occasions.
Why did Mercedes want him?
A move for double world champion Fernando Alonso, or Ferrari driver Sebastian Vettel, who won four consecutive titles at Red Bull, to sit alongside Hamilton would have provided a blockbuster driver line-up. But, following Hamilton's fractious, and at times, bitter relationship with Rosberg, Mercedes have gone for a driver who is likely to provide greater stability within the team as well as possessing the speed and skill required to cement their position as the sport's number one constructor. Mercedes boss Toto Wolff is a long-term admirer of Bottas and he was also part of the Finn's management group.
Is Bottas good enough to challenge Hamilton?
The Finnish driver has been touted as a future world champion by Williams, and, after joining Mercedes, we will now get a chance to see if he can live up to that billing. At the launch of the new Mercedes, Bottas said he would "rather stay at home" if he did not think he could beat his new team-mate. But Hamilton will be desperate to make amends for missing out on the title to Rosberg last year, and the Briton, widely acknowledged as one of the best drivers in the sport's history, also has the advantage and experience of being with Mercedes since 2013. Bottas may have impressed at Williams, but he will face a tall order to match the Briton.
How did Bottas fare in pre-season testing?
After four seasons with Williams, it was only to be expected that Bottas would take time to adapt to a new car. The Finn appeared to struggle with the handling of his Mercedes in the first two days at Barcelona, but he gradually improved as the opening test wore on before providing a glimpse of his potential with the quickest lap of the winter. While both Ferrari drivers usurped Bottas' best effort at last week's final test, the Finn finished pre-season testing with a quicker time than Hamilton. He also covered more mileage than any other driver - clocking up a mammoth 628 laps (nearly 10 race distances) of the Circuit de Catalunya - which will stand him in good stead for the campaign.
What else do we know about him?
Bottas is married to Emilia Pikkarainen, a swimmer who has competed for Finland at three Olympic Games. They tied the knot last September. He also has a burger named after him in Finland. The 'Bottas Burger', served up by a restaurant which sponsored him in his junior career, consists of two steaks, onion, cheese, tomato and mayonnaise.