Demi Moore has formally filed her divorce response to Ashton Kutcher’s previous filing, and her papers reveal a big cheating secret, Breaking Celebrity News is reporting exclusively.

Moore cites the date of separation as November 17, 2011.

EXCLUSIVE DOCUMENT: Read Demi Moore's Response To Ashton Kutcher Filing For Divorce

That's crucial because Ashton hooked up with Sara Leal in San Diego on September 24, 2011 — with Leal claiming that he said he was separated. (Watch this video of Leal, in a string bikini, wildly partying with friends before her hookup with Ashton, even licking a shot off a gal