George Russell has been confirmed at Lewis Hamilton's replacement for this weekend's Sakhir Grand Prix after the seven-time world champion was struck with coronavirus.
The British youngster, 22, is in his second season with Williams, but is a member of the Mercedes junior driver programme.
Silver Arrows' chiefs have been able to come to an agreement with Williams following crisis talks on Tuesday, with Russell's participation confirmed 24 hours after news of Hamilton's positive result emerged.
The British youngster, 22, will make his Silver Arrows debut in Formula One and said: “Firstly, I want to say a huge thank you to everybody at Williams for giving me this opportunity.
"I might be wearing a different race suit this weekend, but I’m a Williams driver and I’ll be cheering my team on every step of the way.
"I see this as a great chance to learn from the best outfit on the grid right now and to come back as an improved driver, with even more energy and experience to help push Williams further up the grid.
"A big thank you also to Mercedes for putting their faith in me. Obviously, nobody can replace Lewis, but I'll give my all for the team in his absence from the moment I step in the car.
"Most importantly, I wish him a speedy recovery. I’m really looking forward to the opportunity and can’t wait to get out on track this week.”
Williams' acting Team Principal, Simon Roberts added: “Our long-term partnership and George’s affiliation with Mercedes is no secret, and so I’m delighted George has this unique opportunity to join Mercedes, the current Constructors’ Champions.
Stoffel Vandoorne, who races for the Mercedes Formula E team and had been scheduled to fly to Bahrain even before Hamilton's positive result, had been touted as the favourite to replace Hamilton.
The Belgian, who raced in F1 for two seasons with McLaren, is one the team's reserve drivers while fellow stand-in driver Esteban Gutierrez also comes with experience at the highest level.
Nico Hulkenberg, meanwhile, has stood in for Racing Point on two occasions this season and is widely regarded as a safe pair of hands.
But it is Russell who won the race to land Hamilton's seat on a temporary basis, with Jack Aitken racing for Williams in Sakhir.
