The 16-year-old, who has featured on 35 occasions for Birmingham's first team during the 2019-20 season, has been strongly linked with a move to Manchester United over the last few months.
Dortmund have also been consistently linked with the youngster, though, and according to Bild, the Bundesliga giants now have an agreement in place with the player.
The report does not mention whether BVB have agreed a deal with Bellingham, who will see his contract at St Andrew's expire at the end of next season.
The midfielder does not turn 17 until the end of next month but has been a key player for the Blues this term, scoring four times and providing three assists in 32 Championship appearances.
Bellingham has already allegedly been shown around United's training ground with the Red Devils seemingly determined to win the race for his signature ahead this summer's transfer window. body check tags ::