Arsenal have sold centre-back Gabriel Paulista to Spanish club Valencia in a deal reportedly worth around £10 million.
He signed a five-year deal and has a buyout clause of €80m, Valencia said.
The move brings an end to a two-and-a-half-year spell for Gabriel at the Emirates Stadium, during which he struggled to lock down a place in Arsene Wenger's XI.
Gabriel joined Arsenal from Villarreal in January 2015 but struggled to settle in the Premier League, in part because he did not speak any English when moving to London.
He only made six league appearances in his first season but became a more regular presence in Arsenal's team in the 2015-16 campaign and finished up with 29 appearances after overtaking Per Mertesacker as a starter.
Last season he was often used as right-back when Hector Bellerin was injured and performed well after Wenger switched formations to a back three, putting in one of his best performances in an Arsenal shirt in the FA Cup semifinal victory over Manchester City.
However, he missed the final after suffering knee ligament damage in the last game of the Premier League season and has yet to return to full fitness.
Gabriel's return to Spain will help trim a bloated Arsenal squad and could signal a stay at the Emirates Stadium for Calum Chambers, who spent last season on loan at Middlesbrough and has also been linked with a move away from the club.
Including Chambers, Wenger still has five senior centre-backs in the squad, while Nacho Monreal and new signing Sead Kolasinac can also play in a back three.