Spain defender Hector Bellerin has agreed to return to Barcelona on a free transfer from Arsenal.
The 27-year-old, who played 239 games for the Gunners, will be contracted to his boyhood club until June 2023.
Barca full-back Sergino Dest, reportedly a Manchester United target,has joined Italian side AC Milan on loan for the rest of the season.
Right-back Bellerin, who joined Arsenal from Barca in 2011, spent last season on loan at La Liga side Real Betis.
The defender featured in pre-season but has not played in any of Arsenal's five Premier League matches.
In a social media post to Arsenal fans, Bellerin said: "It's not always been easy being an Arsenal player these past 11 years, but it's always been an honour to carry the weight of this badge and defend it almost 250 times in front of you all."View more on twitter
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Barca also sold forward Pierre-Emerick Aubameyang to Premier League side Chelsea in a 12m euros deal (£10.3m) on transfer deadline day.
Meanwhile, Denmark striker Martin Braithwaite, 31, has completed a move across the city to derby rivals Espanyol after having his contract at the Nou Camp mutually terminated.
However Netherlands forward Memphis Depay has confirmed he will be staying, despite reports linking him with a move away from the Catalan club.View more on twitter
It marks the end of an eventful summer transfer window for the La Liga giants with Franck Kessie, Andreas Christensen, Robert Lewandowski, Raphinha and Jules Kounde all arriving at the Nou Camp for almost £200m, despite the club being more than £1bn in debt.
The club were initially unable to register their new signings until further cash was released through a series of commercial deals selling off parts of the club's operations - with club president Joan Laporta accused by some of gambling with the club's long-term future.
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