Hans-Joachim Watzke has said he's "very grateful" to Bayern Munich for their professionalism in allowing Mats Hummels to rejoin their rivals this summer.
Hummels left the Westfalenstadion to join Bayern in 2016 but rejoined the Black and Yellows in June. Dortmund chief executive officer Watzke told DPA (h/t Goal's Daniel Lewis) he found it "extraordinary" Die Roten were willing to let their defender leave.
The 60-year-old said: "I am very grateful to Karl-Heinz Rummenigge for having respected the player's will. I thought that was extraordinary. The way in which these negotiations ended was an indication to me how respectfully we are working together at the highest levels."
Hummels grew up in Bayern's academy but left to establish a first-team place at Dortmund in 2008—initially on loan—where he won a historic pair of Bundesliga titles in 2011 and 2012.
Now 30, the Germany international hasn't taken long to adjust back to playing in Dortmund colours, demonstrating some fine passing ability in pre-season:
Hummels also won the DFB-Pokal crown with Dortmund in 2012, as well as finishing a runner-up to Bayern in the 2013 UEFA Champions League final.
Manager Lucien Favre's side have had an active summer transfer window, signing forwards Thorgan Hazard and Julian Brandt, as well as recruiting Paco Alcacer permanently following his loan last term. Left-back Nico Schulz also arrived from Hoffenheim and has impressed in pre-season.
Bundesliga writer Alex Chaffer praised Dortmund's summer business and recently said the foundations are there for the club to launch another run at Bundesliga silverware:
Alex Chaffer @AlexChaffer
@Bundesliga_EN Borussia Dortmund's impressive summer of moves needs nothing more than names: Schulz, Brandt, Hazard, Hummels. Add a fit Reus off the back of his best Dortmund season and Sancho who just continues to improve with every game. Another memorable title race is on the cards.
Bayern signed two new centre-backs this summer as Lucas Hernandez and Benjamin Pavard arrived from Atletico Madrid and Stuttgart, respectively.
Coach Niko Kovac said in July that Hummels left the club because he didn't want to compete for his place in the XI:
"Mats did a great job, especially in the second half of the season. Like [Bayern president] Uli Hoeness said, at the end of the season Mats came to us and asked what the status quo was for the new season.
"Niklas Sule did a great job, he is a starter of the (Germany) national team and with Lucas we bought a player that we want to play centre-back. That doesn't mean anything.
"Competition means the best player will play. In that case, Mats wanted to avoid that. We accept that and the result is that he plays for BVB now."
Former Dortmund and Bayern team-mate Robert Lewandowski also bemoaned Hummels' decision, per DW Sports:
Hummels will find it easier securing his place in Favre's XI and looks likely to partner Omer Toprak in defence, with Dan-Axel Zagadou, Manuel Akanji and Leonardo Balerdi offering support.