Around 20,000 Eintracht Frankfurt fans attended the Nou Camp to watch their side's Europa League quarter final second leg against Barcelona
The German side had only been allocated 5,000 tickets but another 25,000 Eintracht fans without tickets are believed to have travelled to the Spanish city for the game.
And the entire stadium was awash with white-clad German fans on Thursday night.
Some German fans bought tickets off Barcelona season ticket holders, while other Blaugrana members bought tickets for them.
Eintracht fans also bought tickets online before the club tried to stop German supporters flooding the stadium by preventing anyone from buying a ticket online who did not do so with a Spanish bank card.
But it proved to be too little, too late.
And Barcelona defender Ronald Araujo said the club 'have to look at this' after they were knocked out.
Barca were forced to play the first 10 minutes after the break without their most vocal supporters as thousands left their seats in protest at the Frankfurt invasion of the Catalan giants’ stadium.
Serbia international Kostic converted a fourth minute penalty and added another in the 67th with a low drive after Rafael Borre thundered in their second goal in the 36th for a 4-3 aggregate victory and a sensational win at the Camp Nou.
The Catalans, pre-match favourites after a first leg 1-1 draw in Germany last week, missed a couple of chances with Pierre-Emerick Aubameyang but were far less threatening than their opponents who could have added to their tally.
They did score twice in stoppage time through a Sergio Busquets shot and Memphis Depay's penalty after Frankfurt's Evan N'Dicka was sent off but ran out of time for a third goal that would have forced extra time.
Eintracht, who last reached the semi-final stage in 2019 and are unbeaten away from home this season in the Europa League, will now face West Ham, 4-1 aggregate winners over Lyon.
