In a message that left some fans scratching their heads, the star blamed other commitments for his departure.
It is not clear, however, whether he left or was ushered out.
“Due to circumstances beyond my control, it is with deep regret that I am required to state that I am no longer of the band Spandau Ballet,” he wrote.
“And as such I will not be performing with the band in the future.”
“I’ve been a fan of Spandau since 1980 – I’m heartbroken to hear this news,” one follower replied.
“Out of the blue and with no explanation don’t the fans deserve more?” someone else asked.
“Tony, you’re a good and kind man. This news saddens me, but you’ve brought happiness to many, & we’ll meet again some day,” a third wrote.
Yet another response read: “what’s going on guys. Fans would love to know. Very sad after all these years.”
Spandau Ballet previously split up in the 1990s in a spat over royalties, although they reunited in 2009.
They embarked on their last world tour in 2015, with Hadley also competing on I’m A Celebrity… Get Me Out Of Here!
Since making their debut in 1980, the group have racked up seven studio albums; the most recent of which – One More – charged to No7 in 2009.
They have one No1 single to their name – True (1983) – and are also well-known for tracks such as Gold, Only When You Leave and Through The Barricades.
At time of writing, Gary Kemp, Martin Kemp, John Keeble and Steve Norman have not publicly commented on the split.
Express.co.uk has contacted reps for further comment.