The Germany international has returned to his former club following a trio of titles with the Bavarian giants, becoming the latest BVB man to return
Borussia Dortmund chief executive Hans-Joachim Watzke has thanked Bayern Munich counterpart Karl-Heinz Rummenigge for letting Mats Hummels return to Signal Iduna Park.
The Germany international has returned to his former club for a second spell following his time with the Bavarian giants, after the two Bundesliga rivals agreed a deal in June.
The 30-year-old, who won three successive top-flight crowns at the Allianz Arena, came through their junior ranks before signing for Dortmund in 2008, where he also won two titles and reached the final of the Champions League in 2013, coincidentally losing to Bayern.