We got the proof ... on Sunday, Pepa crashed Spinderella's annual Halloween Boo Bash and stuck around to perform their classic cuts "Push It," "Shoop" and "Whatta Man"!!!

Pepa played the cowgirl and Spinderella was dressed as the Beetlejuice ghost host with the most when she hopped out the DJ booth to perform her "Whatta Man" verse.

Spin later told the crowd they had been mending fences behind the scenes ... and this mini-reunion was a step toward rebuilding their foundation. DJ Jazzy Jeff was also on hand for the festivities.

It's one of those hip hop maturity stories ... the iconic trio went their separate ways years ago after Spinderella sued the group over a royalties dispute, and she eventually saw herself sliced from the film biopic.