Hansi Flick welcomed Alonso's appointment as Madrid boss last summer, but he also knew that it might be bad news for Barcelona. Flick had spoken to the former Bayer Leverkusen boss in his previous capacity as Germany head coach and was hugely impressed by the Spaniard's footballing philosophy.
Alonso's arrival also suggested a long overdue change of approach at the Bernabeu. It seemed as if Jose Angel Sanchez had convinced Perez to embrace a more modern style of play that prioritised teamwork over individualism.
However, the president was never entirely on board, even after Alonso's Madrid made an encouraging start to the season, culminating in a 2-1 victory in the first Clasico of the campaign that enabled Los Blancos to open up a five-point lead over Barca at the top of the table.
Consequently, as soon as results took a turn for the worse, and Perez was left with a straight choice between supporting a demanding coach trying to construct something meaningful in Madrid or appeasing a small group of dissatisfied superstars led by Vinicius Jr, the construction mogul decided to abandon the Alonso project after just six months.
However, while Alonso's reputation has essentially been repaired by the mess Madrid now find themselves in, Perez's has been left in tatters. In his desperation, he's now turned to Mourinho to try to fix things - just as he did all the way back in 2010.
Barca will obviously be somewhat wary of Mourinho, who won a Copa del Rey and a Liga title during his previous reign at Real, but they're still unlikely to see his return as anything to be unduly concerned about. They may not be quite as good as they were 16 years ago, but Flick has won back-to-back championships with a united young squad, while the polarising personality that is Mourinho is now walking into a divided dressing room.
We can, thus, expect Barca's band of brothers from La Masia to make mincemeat of Madrid's mercenaries next season.