Alonso joins Barca after terminating Chelsea contract

Alonso has signed a one-year contract with Barca after striker Pierre-Emerick Aubameyang moved in the opposite direction for 12 million euros ($11.96 million) late on Thursday's transfer deadline day.

"FC Barcelona and Marcos Alonso have reached an agreement to sign the player after he terminated his contract with Chelsea Football Club," Barca said in a statement.

"The defender will sign a contract until 30 June 2023 and the buyout clause has been set at 50 million euros."

Alonso, who came through Real Madrid's academy, spent six years at Chelsea after a 23 million pounds ($26.48 million) move from Fiorentina in 2016, returning to the English top-flight after stints at Sunderland and Bolton Wanderers.

The 31-year-old made over 200 appearances for Chelsea and was an integral part of their 2016-17 Premier League title-winning team under Antonio Conte.

Alonso also won the Champions League, Europa League, FA Cup and Club World Cup during his time at Stamford Bridge.

Chelsea, who lost defenders Andreas Christensen to Barcelona and Antonio Rudiger to Real Madrid, signed Marc Cucurella from Brighton & Hove Albion and Wesley Fofana from Leicester City to strengthen their backline.

On a busy deadline day for Barca, Hector Bellerin returned to the club on a free transfer, while Sergino Dest went on loan to AC Milan and Martin Braithwaite joined Espanyol on a free transfer after terminating his contract.

The Catalan club have also brought in Robert Lewandowski, Jules Kounde, Raphinha and Franck Kessie in a busy transfer window, despite being plagued by financial problems.

Barca have sold stakes in their audiovisual studio, their licensing and merchandising division and even part of their LaLiga TV income rights to help balance the books and comply with the league's financial fair play rules.