Chris Brown and Karrueche Tran -- He Says She Banged Drake ... She Plays the 'Mistreatment' Card

Things have gotten even more nuclear between Chris Brown and his ex-girlfriend Karrueche Tran ... and now Drake's been dragged into it, making him the Camilla Parker Bowles in the relationship.

Brown just ripped into Karrueche on Instagram, calling her a cheater, saying, "I was locked up for damn near 4 months and only got 1 visit from you while u was hosting parties and taking secret trips to Toronto, going on dates with Drake."

Chris fired his salvo after Karrueche went on the attack, explaining their breakup this way ... "I refuse to be repeatedly mistreated especially by someone who claims to love me. That's not love."

As if it really needs translation ... Chris is calling out Karrueche, who publicly made it look like she was standing by him when he was jailed earlier this year. As for Drake ... well, you remember W.i.P. nightclub, right? That fight involved Rihanna and the 2 seemed to squash the beef ... but it's clearly back in force.

And as for Karrueche's comment ... after the Rihanna beating, the word "mistreated" has all sorts of meaning when it comes to Chris, and Karrueche knows it.

Karrueche added, "If you can't love me the right way, then don't love me at all."

Short story ... the atomic bomb war has just gone full hydrogen.