Dennis Shields, the on-again-off-again boyfriend of Real Housewife of New York City Bethenny Frankel, has been found dead in his home in Trump Tower.

The 51-year-old died after overdosing on oxycodone, an addictive opioid he was taking to treat back pain.

Shortly before 9am on Friday, Shields asked his maid to buy him Narcan from a pharmacy after taking multiple pills the night before, according to TMZ.

It is not known if the maid ever gave him the drug which reverses the effects of an opioid overdose by knocking out opioids from the opiate receptors in a person's brain.

At some stage before 9am, Shields lost consciousness and the maid called 911. He was pronounced dead by EMTs shortly afterwards.

Sources close to the businessman told that his back had been 'acting up' recently and still hadn't recovered from a 2015 surgery.

They believe that he died of cardiac arrest because his heart 'could not cope' with the dosage of the powerful painkiller.

Frankel was at her home in Bridgehampton when he died. She appeared to be unaware of the tragedy and was uploading photographs and videos to her Instagram story until around noon.

She and Shields dated intermittently from 2016 onwards but always remained friends.

He appeared occasionally on the Bravo show in which she stars. The SkinnyGirl mogul has not commented on Shields' death.

Shields' estranged wife Jill, who he had four children with, told she was 'devastated' by his death.

The pair were married for 26 years before separating in 2016, not long before he and Frankel became an item.

They had not yet finalized their divorce when he died.

'We are all heartbroken.

'Dennis was and always will be the love of my life. His spirit lives on in our children,' she said.

She added that he was a 'loving father and friend.'

The couple had four children together; daughters Tyler, 24, Darien, 20, and Kelsey, who is in college, and one son, Zachary, 23.

Shields was the CEO of LawCash, a Brooklyn-based firm which bankrolls lawsuits against New York City.

He was also the executive chairman of Esquire bank and the fin-tech start-up YieldStreet.

The businessman lived on the 42nd floor of the luxury building in a two bedroom apartment which he bought for $3million in 2012.

He put it on the market in April 2017 for $4.75million and it is still up for sale.

The first of Frankel's housewives to speak out on Friday was Sonja Morgan.

'This is heartbreaking.

'I spoke to Bethenny yesterday to say I was going to Coast Rica, in case she wanted to come and get away.

'She’s been working so much,' she told RadarOnline.

Carole Radziwill, who spent the last season fighting with her one-time best friend Bethenny, later tweeted her condolences.

Without making reference to Bethenny, she said: 'I just heard the sad news about Dennis.

'He was a good man. My condolences to all his family and friends. So tragic.'

Frankel and Shields had been friends for years before they began dating.

She called one of his daughters one of her Bravo show's infamous reunion episodes to prove their relationship was wholesome after it was claimed that they began seeing each other before his separation.

During that call, Shields' daughter spoke of the back surgery which was still causing him pain when he died.

In May, after parting ways, Frankel alluded to a reconciliation, telling Steve Harvey: 'I've been with someone on and off for years.

'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."

'And I think we might be at that point, believe it or not. I haven’t said that to anyone yet.'

On Friday, Shields' colleagues at Esquire mourned him as a 'true visionary'.

'It is with deep sadness that we mourn the loss of our dear friend and business partner, Dennis Shields.

'Dennis' passion for his family, friends, and professional work were unmatched and there are no words to describe the loss we feel today.

'This tragic and emotional loss is devastating to all of us who knew Dennis and loved him dearly,' said Tony Coelho, Vice Chairman of the Board.

Andrew Sagliocca, President and Chief Executive Officer, added: ''Dennis was a great visionary in the financial and legal community and created a tremendous franchise in Esquire Bank.

'Our focus, thoughts, prayers, and love are with his family.'

Shields' death is the second in Trump Tower in six months. In April, an art dealer was killed by a fire in his 50th floor apartment.