The cast members of the "Real Housewives of New York City" are mourning the loss of Dennis Shields, Bethenny Frankel's on-again-off-again boyfriend.

"This is heartbreaking... Dennis is her rock," co-star Sonja Morgan told Radar. "Dennis was important to her, and her daughter. Another tragedy in her life. I’m so sad for her...This saddens me to no end because it seems to be never-ending for her."

Carole Radziwill took to social media to share her condolences tweeting: "I just heard the sad news about Dennis. He was a good man. My condolences to all his family and friends. So tragic."

In a statement to the New York Post, "RHONY" alum Jill Zarin said she was "devastated" for Frankel, who started dating the late banker in 2016.

"I know what it is like to lose someone so soon. It’s unbearable,” Zarin, who lost her husband Bobby to cancer earlier this year, told the outlet. “There is nothing worse than sudden death. You can’t prepare. There is no time to say goodbye.”

Shields was found dead on Friday in Trump Tower in Manhattan, the medical examiner told Fox News. He was 51.

The Medical Examiner's office is currently investigating Shields' cause of death. According to the New York Post, Shields, who was living at Trump Tower at the time of his death, asked his assistant to administer Narcan at 9 a.m. The Post reports he died of a suspected overdose.

Police told Fox News Shields was dead on arrival.

Frankel and Shields appeared together on the Bravo reality series. He was filmed with the popular cast member during the show's most recent season.

Although they started dating two years ago, the SkinnyGirl mogul, 47, and Shields first met in 1988 when he dated and eventually married one of the reality star's high school friends. They reconnected in 2016 after he separated from his wife.

Frankel addressed their relationship in a May interview with Steve Harvey.

“I’ve been with someone on and off for years,” she told Harvey. “It’s like a partnership where if we’re not being teammates and it’s not working and one man is down, then the other man is down. We’re trying to really kind of be good partners and be good teammates and I think relationships oddly are —and this sounds cold—but a little bit like business. If both people aren’t happy about it but slightly uncomfortable and giving up something or giving in [to] something, it doesn’t work. So both partners have to say, ‘All right, I’m in it for this.’”

Frankel added: “And I think we might be at that point, believe it or not… I haven’t said that to anyone yet.”

Fox News' Leora Leora Arnowitz and Sasha Savitsky contributed to this report.