Mainz have announced the signing of defender Abdou Diallo from Monaco on a five-year deal for an undisclosed fee.
The 21-year-old France Under-21 international has put pen to paper on a contract which runs until 2022 with the Bundesliga club.
Mainz sports director Rouven Schroder added on the club's official website: "Abdou Diallo is a strong player and an intelligent fighter who has created a lot of enthusiasm on the European market
"We are delighted that he has decided with full conviction to take his next step at Mainz."
Diallo only made five league appearances as Monaco won the Ligue 1 title last year, and he played in five more games in cups along with one Champions League start.