"The Real Housewives of Atlanta" star Cynthia Bailey is mourning the loss of a dear friend ... famous fashion designer and celeb stylist Kithe Brewer.

Kithe died this week at 60 and Cynthia tells us she's "heartbroken" over his passing.

Cynthia tells TMZ … "He was more than just an incredible fashion designer, he was family to me, like a brother. He was truly a visionary and so far ahead of his time creatively."

The reality TV star says Kithe helped inspire the platinum silver wedding dress she wore on a 'RHOA' episode.

Cynthia is remembering Kithe for being "fearless" with fashion and life, telling us ... "He always encouraged me to embrace my individuality and never be afraid to take risks with my style. I trusted his vision completely because he had such a special gift. Beyond his talent, he was kind, loving, supportive, and deeply loyal to the people he cared about."

Kithe also worked with icons like Beyoncé, Iman, Julianne Moore, and Janelle Monáe ... and Cynthia says, "His creativity and influence will never be forgotten."

The cause of death is unclear.

Cynthia tells us ... "I'm grateful I was able to stand by his side as a friend throughout the years, especially during the times he needed love and support the most. I will miss him deeply, and I pray he is finally at peace."

RIP