Oscar Piastri will drive for McLaren in 2023 after the FIA's Contract Recognition Board ruled in their favour over current employers Alpine.
The verdict, bringing an end to an extraordinary transfer saga and contract battle, means Alpine have lost their highly-rated reserve driver and are still looking for a replacement for Fernando Alonso for next season.
Alpine had been adamant they had a valid contract for Piastri to drive for them in 2023, signed last November, and even announced the Australian's promotion at the start of August. But Piastri, who immediately refuted the team's confirmation, and his management believed he had a deal tied up with McLaren as his Alpine clause had expired.
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The four-person Contract Recognition Board (CRB) met on Monday to start a hearing into the dispute and on Friday revealed they had unanimously ruled in McLaren and Piastri's favour.
Sky Sports News understands key pieces of Alpine contractual paperwork were unsigned by Piastri.
The CRB said Piastri had signed a deal with McLaren on July 4 and was entitled to drive for the team in 2023 and 2024 - and McLaren immediately announced a with a multi-year deal for a new rookie driver to partner Lando Norris.
"I'm extremely excited to be making my F1 debut with such a prestigious team as McLaren and I'm very grateful for the opportunity that's been offered to me," said Piastri.
"The team has a long tradition of giving young talent a chance, and I'm looking forward to working hard alongside Lando to push the team towards the front of the grid."
Alpine said soon after that they now "consider the matter closed" and will announce their driver line-up in due course.
The French team, who are currently ahead of McLaren in an on-track F1 battle for fourth, have their sights set on Pierre Gasly as Esteban Ocon's next team-mate.
Gasly has signed a contract with AlphaTauri for 2023 but Red Bull are willing to release the Frenchman, who had just half a season alongside Verstappen in 2019 before being dropped back down to the sister outfit.
Why did Alpine's case fail? Explaining the big Piastri blow
Sky Sports News' Craig Slater
"In terms of why Alpine were unsuccessful here, I understand key bits of paper perhaps did not have Piastri's signature on it.
"I have also learned that Alpine will have to bear McLaren's legal costs as well as the CRB costs which reflects the weakness of their case in contractual terms.
"The timing of this is fascinating because McLaren signed Piastri on July 4. Nine days later their current driver Daniel Ricciardo, who won't be their next year, announced he would be staying with the team.
"Andreas Seidl said he kept Ricciardo in the loop throughout, but that seems like a bit of a conflict in the timeline and chronology.
"It's a tough one for Alpine to take. They would have invested close to £10million in Piastri's career.
"My understanding is they will now have to have a very careful look at the way they go about their contractual business. One or two individuals connected with that team have observed that Red Bull never make these mistakes when they have young drivers, there's no way another team can come and poach them because they are absolutely watertight in what they do.
"They have announced they are drawing a line under this and they won't be seeking compensation in the high court either.
"The one silver lining from an Alpine perspective is I think during this process they perhaps identified they can get Pierre Gasly from the AlphaTauri team.
"He is a race-winning driver, more experienced than Piastri, and I believe he has ben their more preferred option for at least the last week and I expect him to make the move."
McLaren delighted after landing rising star Piastri
McLaren had always been confident in signing Piastri, having already agreed a pay-off to end Daniel Ricciardo's contract early at the end of 2022.
They have now confirmed one of the hottest properties in motorsport, with Piastri having followed in Charles Leclerc and George Russell's footsteps by winning the Formula 3 and Formula 2 titles in consecutive seasons.
"Oscar is one of the up-and-coming talents coming through the feeder series into F1 and we are delighted to see him join the team for 2023," said McLaren CEO Zak Brown.
"Winning both F3 and F2 in successive rookie seasons is a real achievement and testament to his talent in single-seater racing. In Lando and Oscar we have a young, exciting F1 line-up with a huge amount of potential, standing us in good stead to achieve our future ambitions."
Andreas Seidl added to Sky Sports F1: "There are two reasons why we wanted to have Oscar.
"I think he has shown in the junior categories that he's something very special and has a lot of potential. Plus, also in terms of personality I think he's a perfect fit into our team and that should be the main focus of the news.
"In terms of the Contract Recognition Board, for us, that was never a case therefore I guess it's better that you ask the other party involved why they thought they had a case.
"Therefore this [decision] is not really any surprise for us. It's important now we can look to the future, and at the same time, focus on the final eight races of the season together with Daniel and Lando."
The story of a remarkable transfer saga
While the F1 'silly season' is notorious for contract bombshells, no one would have pictured that what started with Sebastian Vettel's retirement and Fernando Alonso's move to fill his Aston-Martin seat, would turn into two teams battling over a rising young star: Oscar Piastri.
With a space free due to Alonso's departure, Alpine used the opportunity to announce their young driver, Piastri, as his replacement. Piastri, however, insisted his future in the sport lay with another team and not the one who funded his title-laden junior career and his step up to become an F1 reserve driver.
"I understand that, without my agreement, Alpine F1 have put out a press release late this afternoon that I am driving for them next year," posted Piastri on social media.
"This is wrong and I have not signed a contract with Alpine for 2023. I will not be driving for Alpine next year."
Such confidence in Piastri's message made it clear that the young Australian had an agreement elsewhere, and it didn't take long to emerge that that team was McLaren.
A contractual battle was then in play between Alpine, who had insisted throughout they had the rights to their reserve for next year following a contract he signed last November, and McLaren and Piastri, whose camp had been sure an Alpine clause had expired and he could move teams.
McLaren made their stance on Piastri clear when terminating Daniel Ricciardo's contract for 2022, well and truly opening the door for their next young driver to partner Lando Norris.
The CRB's verdict, which came a day later than expected, ends the dispute and leaves Alpine looking for a 2023 driver.
Alpine want Pierre Gasly to fill their empty seat for the 2023 season alongside Esteban Ocon.
Sky Sports News understands if Alpine are prepared to pay a fee, then Gasly would be allowed to leave AlphaTauri and the Red Bull family.