Barcelona have signed midfielder Oriol Romeu from Girona, the club announced on Wednesday, in a deal that sees midfielder Pablo Torre, 20, move in the other direction on a season-long loan.
Romeu, 31, becomes Barca's fourth arrival of the summer following Ilkay Gundogan, Inigo Martinez and Vitor Roque, although the latter will not join until 2024.
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The former Chelsea and Southampton player returns to the club where he spent seven years when he was younger before moving to England in 2011.
After progressing through Barca's academy to make two first-team appearances, Romeu left for Chelsea as a 19-year-old for a fee of around €5 million ($5.6m).
Loan spells with Valencia and Stuttgart followed before a permanent switch to Southampton, where he spent seven years and made over 250 appearances.
Romeu returned to Spain last summer and signed for Girona, where he impressed at the base of their midfield as the Catalan side secured a 10th-place finish in LaLiga.
Barca's interest in Romeu stemmed from their need to fill the vacancy left by Sergio Busquets, who has joined Inter Miami, and the lack of money available to pursue their primary targets.
Sources told ESPN that Real Sociedad's Martin Zubimendi and Bayern Munich's Joshua Kimmich were both names championed by coach Xavi Hernandez, while Marcelo Brozovic, who recently swapped Inter Milan for Al Nassr, was also considered.
However, with Barca operating under strict financial restrictions due to being in excess of their LaLiga-imposed spending limit, they were forced to explore alternatives.
Romeu emerged as their first option due to the cost of the deal, his performances with Girona last season and his knowledge of the club having come through the academy.
He becomes Barca's second midfield signing of the summer following the arrival of Gundogan, adding to options which already include Frenkie de Jong, Pedri, Gavi, Sergi Roberto and Franck Kessie.
President Joan Laporta has said Barca would also like to add another midfielder to the squad, with Xavi previously requesting a "Santi Cazorla-type player" in the final third, but further incomings are likely to be conditioned by outgoings.
Torre, meanwhile, will join Girona on a season-long loan as part of the agreement which sees Romeu sign for Barca.
After joining the Blaugrana from Racing Santander last year, the attacking midfielder, who is only 20, has found regular minutes hard to come by and is need of regular game time in the Spanish top flight.