Cher's paying tribute to the only man who dumped her ... sharing a loving message to Val Kilmer months after revealing the megastar broke her heart back in the day.

The singer-songwriter took to X early Wednesday morning to shout out the actor who she calls "Valus" in her post ... kicking it off by saying he will be greatly missed.

Cher specifically highlights Kilmer's humor ... while joking he's was also a "pain in the ass." She adds he was a great friend, good with kids -- and incredibly brave while battling cancer.

The post comes just a few months after Cher admitted only a few dudes had ever dumped her ... telling Howard Stern men expected -- and received -- mind-blowing sex from her ... and, when the host asked who would ever leave her, Cher responded "Look, I was madly in love with Val Kilmer, and he left."

As for an explanation ... Cher says you're only meant to be with some people for certain chapters of your life -- and, her time with Val had run its course.

As you know ... Val's daughter, Mercedes Kilmer, announced her father's death yesterday -- revealing he'd died after a battle with pneumonia. Val also fought throat cancer over the past decade, an illness that greatly affected his work life.

Kilmer -- star of flicks like "Top Gun," "Batman Forever," and "Willow" -- was 65.