Arsenal have accidentally revealed their new signing after pictures emerged of the player in training with his new teammates.
Omar Rekik was spotted at the club's Colney training ground in St Albans with the development squad.
The 19-year-old was part of a swap deal with Matteo Guendouzi, with the Frenchman joining Hertha Berlin over the summer.
The Gunners already agreed a £900,000 fee with the Germans when negotiations took place during the last transfer window.
That has been knocked down to closer to £500,000 after a deal failed to go through in time.
Guendouzi fell out of favour under Mikel Arteta after repeated acts of indiscipline and Hertha were happy to pick up the former Lorient star.
And going the other way is Rekik, a centre-back who has been touted for big things in the future.
The teenager fuelled speculation that he was Arsenal-bound last month when he posted a photo of him in London.
And on Wednesday, pictures emerged of him training with the Under-23s despite the Gunners announcing his arrival yet.
However, Rekik could be on his way back to Hertha before the end of the month.
Arsenal are said to be taking a closer look at the defender before deciding what is next for him for his development.
It is likely who could be loaned out and the Bundesliga outfit are happy to take him back for the rest of the season.
He has yet to make a senior appearance at the Olympiastadion but is highly regarded by the club's staff.
Meanwhile, fellow young defender William Saliba has already made his debut for new club Nice.
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The Frenchman was signed for £30m but was not included in Arsenal's Europa League squad this season and also did not play in the Premier League.
He was allowed to leave on loan with a return to France following after a move to Nice, where he played in a 2-0 loss to Brest.
The Allianz Riviera outfit, owned by British billionaire Jim Ratcliffe, are 13th in Ligue 1.