According to the pair's mother DIANE, Michael - who is currently divorcing wife MELISSA - was invited to the September (05) event but decided not to attend as a "favour" to his sibling.
Diane describes Michael's actions to US magazine Star as "a favour to Ashton from a loving brother".
She adds, "We were determined to keep the wedding a secret and we thought the best way to do that was keep Melissa out of the loop. Michael was invited."
Last month (SEP05), Melissa blamed Charlie's Angels: FULL THROTTLE star Demi for Michael's absence.
She said, "I've always felt that Demi thinks Ashton's family is working class and uneducated and not sophisticated enough to be around."