Romero, who was vice-captain under Postecoglou and a key figure in the squad, wrote on Instagram: "Ange, thank you for these two incredible seasons. You’re a fantastic coach, but above all, a great person who deserves the best.
"From day one you paved the way despite the many obstacles that always existed and always will exist. Beyond everything, we won a trophy and went down in the history of this beautiful club, which is the only thing that matters.
"I wish you the best because you deserve the best, and thank you for everything."