The 18-year-old Brazilan playmaker becomes the second player from Real to make a similar move after Achraf Hakimi enjoyed a meteoric rise during his two-year stint in the Bundesliga.
"I am happy to be with BVB now. The club is known for betting on young players and making them better," he said after completing the move to the German giants on Wednesday.
"I want to learn a lot here, play a lot and help the team to be successful. I hope that we will have many happy moments together."
The teenage sensation scored six goals in 14 Serie A games for Flamengo before joining up with Real's B team at the turn of the year before the coronavirus enforced suspension of football.