Postecoglou parted ways just over two weeks after guiding Spurs to a historic Europa League triumph.
The shock dismissal comes despite Postecoglou ending the club's 17-year wait for silverware, having led them to victory in the Europa League final. The triumph had been seen as a turning point, but Tottenham's dismal domestic form ultimately proved his undoing.
Spurs finished 17th in the Premier League - their worst league finish since the competition began in 1992 - and lost 22 of their 38 matches. Despite European success, the club narrowly avoided relegation, prompting concerns over the direction of the team under Postecoglou.
Appointed in 2023 following a highly successful stint with Celtic, Postecoglou was initially praised for instilling an attacking philosophy and bringing renewed energy to the squad. However, the team's Premier League collapse led to mounting pressure.
"Gaffer. You've changed the trajectory of this club," Son posted on Instagram.
"You believed in yourself, and us, since day one and never wavered for a second. Even when others did.
"You knew what we were capable of all along. You did it your way. And your way brought this club the best night it's had in decades. We will have those memories for life.
"You trusted me with the captaincy. One of the highest honours of my career. It's been an incredible privilege to learn from your leadership up close. I am a better player and a better person because of you.
"Ange Postecoglou, you are a Tottenham Hotspur legend forever. Thank you, mate."
The Europa League win had momentarily lifted the gloom over north London and ended a trophy drought dating back to the 2008 League Cup. Yet the club's league collapse ultimately sealed Postecoglou's fate.
England manager Thomas Tuchel expressed shock and sympathy after Tottenham Hotspur sacked Ange Postecoglou just 16 days after the team won the Europa League, ending a 17-year trophy drought.
Ange Postecoglou has been sacked as head coach by Tottenham Hotspur despite the Australian mentor guiding the club to their first trophy in 17 years.
Tottenham Hotspur have kicked off their transfer window with the signing of Kevin Danso from RC Lens and confirmation of five first-team exits, including the sale of Pierre-Emile Hojbjerg to Marseille.
Christopher Nkunku could be on the move this summer, with reports suggesting the Chelsea forward is open to a return to Germany or a new challenge within the Premier League.
