👋 #BemVindoReinier 🇧🇷
— Borussia Dortmund (@BVB) August 19, 2020
The 18-year-old joined Madrid from Flamengo for €35m in January and has been playing for their second team.
For the next two seasons he will play in Germany at a club famed for its talent development.
“Reinier is a player who possesses enormous talent and can be deployed in various attacking positions,” sporting director Michael Zorc said. “We’ve been keeping tabs on the lad for over two years; in addition to his outstanding technical qualities, he also boasts a strong physical presence.
“Following the long break from competitive football, we’ll give him the necessary time to adapt to professional football in Germany and he can then be an additional option for us going forward.”
Reinier, an attacking midfielder, hopes to take advantage of Dortmund’s reputation for improving young talents.
He said: “I’m happy that I’m now at BVB. The club is known for its focus on young players and improving them.
“I would like to learn a lot and play a lot here, help the team and be successful. I hope that we’ll experience many happy moments together.”