Mary Cosby has paid tribute to her son Robert Cosby Jr. ... a couple days after confirming his death earlier this week.

Check out the "The Real Housewives of Salt Lake City" star's latest IG post -- she shared a throwback picture with her son and remixed cover of Cyndi Lauper's "Time After Time" playing over it. She remembered him with a touching caption that reads ... "#godfirst #love #forever #❤️ I'm Going to miss you bubs❤️🙏😢."

Her 'Housewives' family shared an outpouring of support in the comment section, with Kyle Richards, Heather Dubrow, Cynthia Bailey and more sending their love and condolences.

We broke the sad news ... Robert died Monday after police responded to a Salt Lake City residence for a possible overdose, which turned into a death investigation upon arrival. We reported Narcan was administered by authorities at the scene.

Robert had been in the news over the last year due to various personal struggles, including his ongoing divorce from wife Alexiana Smokoff, an arrest last fall for trespassing, assault, and more, and a subsequent stint in jail.

This week, we also learned he was charged with felony aggravated assault and felony assault earlier this month.

Robert was only 23.

RIP