Sid Wilson's Behavior Toward Bandmates Led to Slipknot Firing

Sid Wilson's exit from Slipknot may have stunned fans ... but his bandmates had been ready to pull the plug for quite some time ... TMZ has learned.

Sources with direct knowledge tell TMZ ... the decision came after the group finally had enough of Sid's behavior ... namely, the way he treated his bandmates.

We're told the firing was a long time coming -- not some abrupt decision made in the heat of the moment.

In fact, our sources say Slipknot was planning to announce Sid's departure this week ... but the band lost control of the rollout when we first reported Friday the group's longtime DJ and keyboardist had been permanently kicked out.

We're told the early reveal caused the band to freak out behind the scenes ... with members frustrated they could no longer announce the split on their own terms.

We broke the story ... Sid was informed Friday afternoon that he was officially out after more than 25 years with the heavy metal group.

He joined Slipknot in 1999 and was one of its nine original members.

The firing comes on the heels of his split from Kelly Osbourne back in March.

They quietly called off their engagement ... but our sources have said there's still a chance they could get back together.

Sid resurfaced Sunday outside a Los Angeles recording studio ... but he kept his head down and stayed silent when asked point-blank about the firing.