A cause of death has yet to be determined.
Police responded to a 911 call of an unconscious man inside Trump Tower about 9:19 a.m., officials said in a press release.
An emergency medical service team pronounced Shields dead at the scene.
Bethenny Frankel has not made a public statement regarding Dennis Shields.
"This is really bad". I'm so sad for her.
In February, a source told PEOPLE the pair weren't together, but said Dennis was an important part of the RHONY star's life.
Shields, who had been friends with Frankel for almost 30 years before they began dating in 2016, lost consciousness before the medication could kick in.
Our thoughts are with Dennis' loved ones at this time. "His spirit lives on in our children".
Law enforcement sources told TMZ that Shields' assistant had tried to give him Narcan to revive him but the effort was unsuccessful.
In May, the reality TV star told Steve Harvey that their relationship was complicated, according to People. "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".
Frankel's on-off romance with Shields was a mainstay on Real Housewives of NY.
Bethenny Frankel has been active in the news lately and on social media as she comments regularly on episodes of RHONY and the recent cast shake-ups.
She added that they were trying to be good teammates and partners, and she thinks that relationships are "a little bit like a business".