Mary called him 'Gramps' growing up. Then her grandmother died and she married him.

When The Real Housewives of Salt Lake City (RHOSLC) first aired in 2020, Mary Cosby captivated audiences and quickly became a fan favourite.

The 53-year-old preacher has long been one of the most baffling figures in The Real Housewives franchise. Known for her candid comments, she dressed in high fashion, all while serving as the first lady of Faith Temple Pentecostal Church.

But the newfound fame came with a darker side. Soon after the series began airing, she and her husband, slash former step-grandfather (yep, you read that right), were hit with accusations the congregation they claimed to lead was a cult.

A new TLC docuseries, The Cult of the Real Housewife, has pulled back the curtain on the questions that have followed Mary for years. It examines the allegations surrounding her church, her power and the blurred lines between faith, fame and control.

It also casts light on Mary's controversial marriage.

Watch the trailer for The Cult of the Real Housewife here. Post continues below.

A marriage under the spotlight.

Mary, who returned to the full-time RHOSLC cast in Season 5 after stepping aside at the end of Season 2, is one of the few women on the show who is not part of the Mormon faith. Instead, she's described as a "Pentecostal First Lady".

In 1997, Mary's grandmother, Rosemary Redmon Cosby, also known as "Mama," passed away, leaving her millions of dollars, businesses and her family's Pentecostal mega church.

Mary has long claimed that to receive her inheritance, her grandmother decreed she had to marry her step-grandfather.

Rosemary had been married to Bishop Robert C. Cosby Sr for 22 years. He was significantly younger than her and was her second husband (making him Mary's step-grandfather).

Image: Bravo.

Mary married him when she was in her early 20s, and Robert was in his 40s.

"My grandmother told me, for herself, that she wanted me to take her place," she said on the reality TV show, before explaining Rosemary's reasoning.

"Basically, Robert Sr was 20 years younger than my grandmother. My grandmother felt like she robbed his youth.

"So she said, 'If something ever happens, I want you to marry one of my girls, because I know that they will be loyal to you and treat you good like you treated me.'"

Mary admitted that she didn't want to go ahead with the "arranged marriage."

"I did marry him. I didn't want to. That's weird to me," she said.

"But [my grandmother] really did want me to, so I obeyed her.

"I trusted every word. If she managed to bring this church this far, then she had to be right. And look at my life."

Mary said she sat on the idea before going ahead with it.

"It took us two years to actually marry," she continued. "I had to be certain. I started to pray myself, I started to seek high help myself. When I did that, I felt peace with it, so I married him. I chose what the man upstairs told me to do."

She also had a child with him: a teenage son named Robert Jr.

Docuseries paints marriage in a new light.

In The Cult of the Real Housewife, Mary's estranged sister, Denis, cast doubt on Mary's "inheritance."

Denis claims that Mary started spending more time with Robert Sr — whom they called "Gramps" — soon after Rosemary's death and that Robert Sr bought Mary a BMW. She also claimed her sister had been "disfellowshipped" from the church by her grandmother for being a "troublemaker."

"Some of the things that she's saying about it being an inheritance ... [it] is one of the biggest lies that she's told," Denise said in the docuseries. "For [Robert Sr] to allow her to get on TV and say, 'Mama wanted her to have this and that and the other,' he knows better."

The marriage is said to be one of the catalysts for Mary's estrangement from her mother, Rosalind, who died in 2025 as the documentary was being filmed.

In the docuseries, investigative journalist Cheyenne Roundtree appeared to uncover court documents proving Mary married Robert Sr 19 days after divorcing her first husband, Dana.

On the Season 1 reunion of RHOSLC, Mary told host Andy Cohen there was no overlap between her two marriages.

"The timeline shows there was some crossover happening," Cheyenne said in the docuseries. "Mary's not telling the full story about what happened."

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What Mary has said about the docuseries.

Since the documentary aired, Mary has shared footage of herself and her castmates on Instagram.

However, the hashtags used on the post were the most telling: "#godfirst #love #you #blessed #don't believe the lies. Happy Sunday," she captioned the January 4 post.

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Despite the judgment Mary has copped over her controversial marriage, she's previously insisted they are happy.

"You can't say or do anything to take happiness away from me," she said during the show's reunion.

"It's hard to get. If you can find that in a man, it doesn't matter where he came from."

Mary Cosby has returned to the Real Housewives franchise. Image: Hayu.

The raw moment is sure to be one of the most important plot points, as Mary keeps her cards somewhat close to her chest on the show.

Despite the accusations, the Faith Temple Pentecostal is still in operation; despite closing for many years for renovation, it re-opened in 2025.

You can watch all four seasons of The Real Housewives of Salt Lake City (and every other Real Housewives franchise) on Hayu.

You can stream The Cult of the Real Housewife on HBO Max and discovery+.

Feature image: Bravo.