Video: Dortmund crowd sing 'You'll Never Walk Alone' in tribute to fan who died during game
Borussia Dortmund president Reinhard Rauball said his club's thoughts were with the family and friends of a fan who died during their 2-0 win over Mainz in the Bundesliga on Sunday.
One fan passed away and another was in a stable condition in hospital after they both suffered heart attacks at the Westfalenstadion.
"In the name of Borussia Dortmund, I wish to express my heartfelt sympathy and condolences to the families of those affected," Rauball told Sky Sport Deutschland.
"Our thoughts are with them."
Fans of both clubs fell silent when the news filtered through that the fan had passed away.
Dortmund's Japanese midfielder Shinji Kagawa did not even celebrate the goal which earned Dortmund all three points, with football not on anybody's mind by that stage.
"We were informed pretty quickly in the stands of what had happened," Rauball said.
"From that moment on, the game fell right into the background. I could no longer concentrate on it.
"The fans' reaction was spontaneous. I've never experienced anything like it.
"I can only pay a huge compliment to all of the fans for the way in which they expressed their sorrow and respect in this way, in a unified manner.
"I take my hat off to the Mainz fans who, without exception, joined us in mourning and stopped supporting their team.
"The scarves held in the air when 'You'll Never Walk Alone' was sung has my utmost respect. It shows how deeply rooted honour and respect of each other exists and can be expressed in such a short period of time, and I can only take my hat off to that."
Most Bundesliga clubs immediately showed their solidarity with Dortmund and paid their tributes to the deceased in response to a Tweet by Dortmund which confirmed what had happened.
Dortmund's players lined up arm in arm in front of the Sudtribune - South Stand - as You'll Never Walk Alone was sung by the entire stadium following the final whistle.
"Prayers & thoughts to the fan we sadly lost today at the stadium, as well as to our 2nd fan now at hospital," tweeted Henrikh Mkhitaryan.