Los Blancos owned 50% of his rights.
Atletico de Madrid completed the signing of Mario Hermoso this Thursday. Hermoso was playing for Espanyol but Real Madrid owned 50% of his rights even though he never made his debut with the first team. That means that Los Blancos earned €12.5 million with this transfer, given that Atletico spent €25 million to sign Hermoso away from Espanyol.
Real Madrid had an option to buy Hermoso back for just €7.5 million and he was rumored to be a target until Los Blancos decided to sign Militao. All in all, Hermoso completed a brilliant 2018-2019 season which allowed Madrid to make some profit, something which is particularly important this summer if Los Blancos want to keep improving their team.
Hermoso is a solid center-back who can play as a left-back as well, so he will surely be a useful player for Diego Simeone, even more so after the departure of Diego Godin to Inter Milan.