Mary Cosby Opens Up About Marrying Step-Grandfather Robert Sr.

As Mary Cosby prepares to reopen her church on The Real Housewives of Salt Lake City, she’s shedding new light on how her marriage to step-grandfather, Robert Cosby Sr., was initially architected to install her as the house of worship’s first lady.

Mary toured the results of Faith Temple Pentecostal Church’s years-long renovation with her cousin (and the general contractor) “Big Joe” on RHOSLC Season 6, Episode 4. While taking a moment to reminisce in a pew, she told him that she was “excited” to return to the church, especially because she believed “some prayer” could “help” her son, Robert Cosby Jr., as he navigates his post-rehab journey. 

And Mary is no stranger to the power of prayer, thanks, in part, to her grandmother, Rosemary “Mama” Cosby, who founded the church.

“Because that’s what happened to me,” she explained. “When I was younger, I remember Mama called me and she was like, ‘Mary, I think it’s time for you to come back and be saved and get in church.’ And I was like, ‘OK.’ And because of her, I am everything I am.”

RELATED: Mary Cosby’s Son Robert Jr. Speaks Out on the Difficulties of His Post-Rehab Journey

In order for Mary to take the torch she was being passed, she was told to marry her grandmother’s second husband, Robert. Sr., who serves as bishop, upon Rosemary’s death in 1997. She said they both recognized the unconventional nature of the relationship, but respected her final wishes, nonetheless.

“That was odd to both of us,” Mary admitted. “Marry me? He obeyed what Mama wanted. He wasn’t trying to do anything extra.”

Inside Mary Cosby’s “hurtful” estrangement from her mother

Not everyone was on board with Mary stepping into her grandmother’s role, however — including her own mother, Rosalind. 

When Big Joe mentioned that Mary “battled the storm,” she responded, “For some reason, my mom thought she was supposed to take everything over. How? … My mom, she wanted her way, and she couldn’t get her way.”

As Mary elaborated in a confessional, “My grandmother told her, so we were all clear of what my grandmother wanted. But once my grandmother passed, my mom just started trying to take over everything. And things got bad.”

Both Mary and her cousin went on to detail how Rosalind was “escorted out” of the church by police when she tried to take over the service one day. The two were still estranged when Mary’s mother died in January 2025.

RELATED: Mary Cosby Sheds New Light on Husband Robert Sr.’s Role in Robert Jr.’s Sobriety Journey

“And the fact that it’s full circle now and she’s gone, I don’t know how I feel about that,” Mary shared with her cousin. “It’s like a roller coaster. It hurts. But it’s also a chapter that’s closed. … I feel like it was a storm or a battle that I had been in for all those years.”

Through tears, Mary claimed that, prior to her death, her mother had “put lies out there” in the media about her and Robert. Sr. 

“When my mom walked out of my life, I felt that absence,” Mary concluded to a producer. “But my mom didn’t wanna speak to me, and so I gave her what she wanted. And when she left the earth a few months ago, it almost felt like it was actually official, because it became a whole bigger real hurtful reality.”

How Robert Cosby Sr. supports Mary Cosby today

Meanwhile, after marrying in September 1998, Mary and Robert Sr. are still together today. Earlier on RHOSLC Season 6, Mary opened up about how Robert Sr. played a key role in Robert Jr.’s sobriety journey.

“I didn’t have a support system with him. I just had Robert Sr. I just have one,” Mary explained to her castmates during Episode 2’s RV camping trip. “I couldn’t have done it without Robert Sr. I couldn’t have done it at all.”

After Robert Jr. completed a 30-day rehab program, Mary recalled her and her husband sitting him down for a frank conversation.

“Robert Sr. told him, ‘We cannot babysit you. You have the tools, and you know what you need to do,'” Mary shared with a producer. “So, we, like, made a pact that we would take one day at a time, and we’re letting him figure it out. And that’s how I deal with him.”

Get more details on Mary’s family life today.