DEMI MOORE has finally filed HER divorce response to ASHTON KUTCHER’s filing and it contains a  BIG cheating secret!

In the legal filing Moore cites the date of separation as November 17, 2011 which is critical to her case because Ashton hooked up with Sara Leal in San Diego on September 24, 2011 — with Leal claiming that he said he was separated.

But Demi’s papers show that she certainly thought they were still together while he was off with the other woman!

(Ashton hooked up with Leal on his six-year wedding anniversary to Demi!)

And now Demi, 50, wants Ashton, 35, to pay. She is seeking spousal support from the uber-wealthy thesp and wants Kutcher to pay her legal bills. She cited irreconcilable differences as the reason for the breakup. Kutcher, who filed for divorce in Dec. 2012, may  be headed to a trial with his ex, RadarOnline noted.

 Both come to the table with legal powerhouses, as Kutcher is represented by attorney-to-the-stars Laura Wasser, while Moore has hired New York-based William Beslow.

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