Amber Rose and rapper Just Brittany are joining forces at SlutWalk ... where Brittany will share in detail her alleged vicious beating at the hands of her BF.

Our Amber sources tell us ... Amber reached out to Just Brittany Friday by phone for a couple hours ... and Brittany agreed to be Amber's guest at the third annual SlutWalk October 1 in L.A.

We're told Amber was devastated when she heard the story of an hours-long beating, allegedly at the hands of Brittany's rapper bf Z-Ro back in April. Brittany will get a platform to encourage women not to be deterred by slut shaming after reporting domestic abuse.

Brittany's had insults hurled at her across social media -- from "you're just a rapper whore" to "that thot ass bitch get this man locked up for some shit she claim happened 3 months ago. Suck my d**k and die slow hoe." Cops say she has an audio recording of the beating.

Amber -- who in 2015 broke down talking about exes Kanye West and Wiz Khalifa -- will let Brittany defend herself.

BREAKING DOWN
TMZ.com