Eliaquim Mangala has joined Valencia from Manchester City on a two-year deal that takes him to the summer of 2021.
The 28-year-old centre-back has a contract with the Premier League champions until the end of this season, meaning his first year back at the Mestalla will be on loan.
He will then become a permanent Valencia player at the end of this season, following the expiry of his contract with City.
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The French defender had previously been loaned out to Valencia by City during the 2016-17 season, following a disappointing two years at the Etihad Stadium after his big-money move from Porto in 2014.
He made 33 appearances in all competitions for the Liga outfit, scoring two goals and receiving one red card as they recorded a disappointing 12th-placed finish in the Spanish top flight.
Mangala spent a brief spell with Everton two seasons ago but returned after struggling with injury and subsequently failed to make a single senior first-team appearance at his parent club, featuring five times for City's reserve side in the Premier League 2.
His £42 million (€45m/$51m) price-tag at the time made him the most expensive defender in the world, although he would go on to feature just 79 times for Manchester City in all competitions, with just 57 Premier League games to his name.
In his time in Manchester, City finished second behind Chelsea in the Premier League and then a disappointing fourth as Leicester City shocked the football world with the unlikeliest of league triumphs, before a successful 2017-18 campaign in which City won both the league and the League Cup.
He also won the League Cup with City in his second season in England as they beat Liverpool in a penalty shootout following a 1-1 draw, although Mangala was not included in the squad that contested the final, with Vincent Kompany and Nicolas Otamendi starting, while Martin Demichelis was on the bench.
Mangala came through the ranks with Belgian outfit Standard Liege, moving to Porto in 2011 after making just shy of 100 appearances in all competitions for the club, and moved on again three years and two league titles later, having scored an impressive 13 goals in 95 appearances for the Portuguese side.