The history between Spanish defenders Gerard Pique and Sergio Ramos is well-documented, but it seems to be never-ending.
Ramos is, of course, the captain of Real Madrid while Pique is the cornerstone of the Barcelona defence, but their rivalry has gone way beyond that.
It's a little bit strange considering all that they have achieved together at international level, too.
Both men are World Cup and European Championship winners and are still important parts of today's Spanish squad.
Last month, Spain defeated Italy 3-0 at a typically partizan Santiago Bernabeu, but there were hardly any boos for Pique.
Ahead of that World Cup qualifier, Ramos, Dani Carvajal and Nacho - three Real Madrid players - all called for the public to refrain from whistling the Barcelona player despite his opinions on Catalan independence.
The crowd agreed to their plea and it made for an electric atmosphere as Spain eased past the 2006 World Cup winners.
However, with a referendum for Catalan independence taking place on Sunday, Pique sent out an untimely tweet that has rubbed Ramos and co. the wrong way.
"Pique's tweet isn't the best thing if you don't want to be whistled," the Real Madrid captain said on the matter, according to Marca.
"Maybe the tweet is not the best thing for the [Spain] group, but everyone is free to say what they think."
Ramos is clearly disappointed with Pique and after the public support he offered him, it comes as no surprise.
The pair are set to link-up with the Spanish squad on Monday and manager Julen Lopetegui would be wise to nip the matter in the bud when he sees the players.
The result of the referendum could have a great bearing on the future of Spanish football. If Catalonia were to operate as a sole nation, many of today's stars - Pique included - would represent them instead of Spain.