Paris Saint-Germain have signed Abdou Diallo from Borussia Dortmund, the French side announced on Tuesday.
Diallo moves to the Parc des Princes in a €32 million (£29m/$36m) deal, ending his stay with Dortmund after just one season.
The centre-back joined Dortmund from Mainz ahead of the 2018-19 season and made 38 appearances across all competitions in his only campaign for the club.
The 23-year-old has signed a five-year contract with the club, as he makes the move back to France, with Dortmund sporting director Michael Zorc stating that the defender was in search of a new challenge.
"It is a great honour to be involved with such a prestigious club as Paris Saint-Germain," Diallo said.
"I have always said that the Parisian project was very attractive. Joining the capital club is another important step in my career.
"I am committed to giving my all for my new club and look forward to bringing my qualities and desire to this team renowned for its high quality and high ambitions."
Formerly a part of the Monaco academy, the French defender now moves to rivals PSG to add a bit of youth to the club's back line.
Diallo made 10 appearances in Ligue 1 before moving to Germany, making five appearances for AS Monaco during both the 2014-15 and 2016-17 seasons ahead of his move to Mainz.
Both Thilo Kehrer and Presnel Kimpembe are also counted among the club's central defensive options, and all but Thiago Silva are under the age of 26.
PSG have also signed Ander Herrera and Pablo Sarabia this summer, making Diallo the third addition following deals for the two midfielders.
The French champions have been dealing with a tumultuous summer, headlined by reports that Neymar could leave the club for Barcelona.
After missing the opening days of pre-season training, Neymar reported to Paris on Monday as he began preparations for the new season.
Dortmund have already added to their own back line with the return of Mats Hummels, who came back after originally departing for Bayern in 2016.
The club also has Omer Toprak, Manuel Akanji and Dan-Axel Zagadou among their back line options after finishing second behind Bayern last campaign.