Chelsea and Manchester City fans clashed on the streets of Madrid on Tuesday in unsightly scenes, with baton-wielding police forced to intervene.
The scuffles broke out in the Plaza Mayor square in the Spanish capital and were caught on camera, with clips of drinks being thrown quickly surfacing online.
It was reported earlier this week that Madrid police would be 'on alert' ahead of the 'double danger' of two English supporter bases converging in the same place.
And, in shocking fashion, tensions between them reached breaking point, meaning they had to be separated into different areas of the popular landmark.
Around 8,000 supporters were expected to jet out from England to Spain to watch the Champions League quarter-final showdowns, sparking safety concerns.
Chelsea faced Real Madrid at the Bernabeu on Tuesday night, just 24 hours before City's second leg at Atletico Madrid's Wanda Metropolitano stadium would begin.
In footage posted on social media, the rival fans were seen confronting one another while shouting, before punches were thrown and drinks were hurled.
It was at that point that the police officers charged in to attempt to restore order.
Spanish television channel La Sexta broadcast footage showing armoured officers corralling City fans into one of the many bars in the square to prevent confrontations.
Radio MARCA also filmed the police moving in to break up the thugs.
The Plaza Mayor was identified as a 'hot zone' for police, reports in Spain said, with the area the most 'delicate' place in the city for supporters to gather pre-match.
Manchester United supporters 'invaded' the public space last month, when their side drew 1-1 with Atletico in their last-16 Champions League tie.
Chelsea were left deflated after winning 3-2 in their tie on the night, only to crash out of the competition 5-4 on aggregate after goals from Rodrygo and Karim Benzema.
City, meanwhile, take a narrow 1-0 lead to Atletico on Wednesday evening and no doubt the local security forces will be on alert in case of any more trouble.
City are playing for the right to take on Real Madrid in the semi-final of the competition they so desperately want to win for the first time.