Abdou Diallo has become Borussia Dortmund's second-most expensive signing after his arrival from Mainz on a five-year contract was confirmed.
Dortmund are understood to have shelled out €28 million (£25m/$33m) to snare the centre-back, eclipsing their outlay for Henrikh Mkhitaryan but falling short of the €30m (£26m/$35m) spent on Andre Schurrle in 2016.
Diallo impressed in his solitary season for Mainz, making 30 appearances in all competitions following his arrival from Monaco for a reported fee of just €5m.
"After getting to know the Bundesliga at Mainz, I am looking forward to the challenge of being able to prove myself at a club as big as Borussia Dortmund," the 22-year-old said.