The “All the Queen’s Men” cast and crew is falling apart worse than Humpty Dumpty … show creator Christian Keyes has just been hit with a nasty legal letter — claiming he’s been defaming one of the show’s stars, and warning him to take it back and apologize … or else!

TMZ obtained a copy of a cease-and-desist letter laying out all the drama … Skyh Alvester Black — who plays Addiction Anthony on the BET+ drama — hired Marty Singer‘s law firm to send Keyes some serious demands as Keyes’ “first and last chance to avoid litigation.”

This all apparently stems from a Facebook post last month where Keyes called out Black for allegedly being high as a kite on set … and Black is pissed!

Keyes says, “You don’t get to show up inebriated and brag about it, so yeah … Alvester Black won’t be back. Skyh won’t be back. He will be written out for that and other reasons.”

In the documents, Black’s attorney labels these statements as “textbook defamation,” and says he believes Keyes only made the remarks because Black called out Keyes for repeatedly bullying cast members on set.

Skyh says that bullying included Christian yelling at him, and claiming he was high, in front of 300 cast and crew members.

Interestingly, in the posted video, Keyes actually admits being “abrasive” when he chewed out an unnamed actor for going off-script, or as he put it … “You’re not supposed to be adlibbing, and this is MY show, this isn’t the standup comedy hour.”

The letter demands Keyes remove the social media posts, post an immediate retraction and apology, and permanently cease and desist any further false and defamatory statements about Black.

The Facebook post appears to have been taken down, but there is still a YouTube video showing the Keyes’ tirade. The YouTube channel doesn’t appear to be run by Keyes but Black’s lawyers are insisting their demand applies to Keyes and “anyone acting in concert” with him.

Keyes also doesn’t seem to have issued a public apology as of yet.