Meredith Marks showed Mary Cosby a little love during a DJ set overseas ... with a touching tribute to her BFF and reality TV costar following her son Robert Cosby Jr.'s death.

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The 'Real Housewives of Salt Lake City' star was spinning tunes at the Mighty Hoopla music festival in the United Kingdom when she cued up the choir version of Madonna's "Like a Prayer" while a 'RHOSLC' scene of Mary speaking at church played behind her.

As we reported ... Mary's son Robert Jr. died in February at just 23 years old. His cause of death is still unclear, but we know cops found him while responding to a possible overdose.

Mary's castmates have been showing her support during this difficult time ... with Lisa Barlow, Heather Gay, Whitney Rose, Bronwyn Newport, Angie Katsanevas, Britani Bateman, and Meredith all attending Robert Jr.'s March funeral in Utah.