"Love is Blind" star Mark Anthony Cuevas dropped a bomb on Instagram overnight ... that his marriage to Aubrey Rainey was over -- but it seems he forgot to tell her!

In his message, Mark said the couple had made the decision to split "a few weeks ago," but they would continue to co-parent and focus on their two children.

But ... it seems like he forgot to share that huge update with someone important before posting to the world ... namely, Aubrey -- who replied in the comments ... "This is news to me. lol."

Needless to say, other commentors started blowing Mark up, demanding to know why he would post something like that if Aubrey truly was unaware or was not ready for the news to be public.

As you may recall ... Mark appeared on the first season of "Love is Blind," but he met Aubrey afterward -- the 2 eventually married and had 2 sons together. They were also getting death threats back in 2021, which Mark addressed on his socials at the time.