"My mom's my best friend. She stuck by me through so much. I don't know what I would do without her," Kathryn Dennis previously told PEOPLE

Allison Calhoun Dennis, the mother of Southern Charm star Kathryn Dennis, died Wednesday after an extended illness. She was 59.

Reps for Kathryn did not respond to PEOPLE’s request for comment, but a source close to the reality star confirmed the news Thursday.

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“Their family requests privacy while they mourn with the sad loss,” a source close to Dennis told PEOPLE. “They’re very private people and they want their time to cope.”

Kathryn told PEOPLE in April she was “incredibly close” with her mother, who was a descendent of the seventh U.S. vice president, John C. Calhoun.

“My mom’s my best friend,” Dennis said. “She stuck by me through so much. I don’t know what I would do without her.”

Allison was retired after working at Santee Cooper water service. She had previously battled cancer and moved in with Kathryn during that time.

Image zoom Tommy Garcia/Bravo

“She was sick for a year and a half and I was taking care of her,” Kathryn told PEOPLE. “She’s since been living with me, essentially. It’s great to have her around, especially because she’s so good with the kids [Kathryn’s son St. Julien, 3, and daughter Kensie, 5]. She’s amazing. She’s the best mom I could ever hope for with everything.”