Gene Simmons -- The Smart Ass Wedding Announcement

Gene Simmons is finally revealing what Shannon Tweed told him when he asked for her hand in marriage ... and SHOCKER ... she didn't say no.

Now, the couple is planning the wedding -- and they've already sent out invitations -- complete with a sarcastic wedding announcement from their kids.

The announcement says, "After 28 years of loose strings, our parents have finally decided to tie the knot."

"Our mother will share our horrendous hyphenate of a last name and our father's life ... well, it doesn't change that much."

It continues on a heartfelt note -- saying, "But we will be united as a family in spirit and in title forever."

The wedding is set for October 1 at the super-fancy Beverly Hills Hotel. Check out the invitation for the dress code ... funny stuff.