ONE of the world’s most prolific serial killers Sergey Tkach has died in Ukraine.

Prison officials suggested that he “died from a broken heart” after his young wife stopped visiting him.

6 Tkach is shown being locked in a tiny space behind bars during his interview in the documentary Credit: Netflix

Convicted of the murders of 37 women between 1980 and his arrest in 2005, but suspected to have killed a further 100, Tkach, 66, died from heart failure in Zhytomyr Number Eight colony in Northwest Ukraine on Sunday.

Tkach’s remains have already been buried in an unmarked grave in a cemetery decimated to homeless and persons who cannot be identified are buried in Zhytomyr, according to a prison official, who did not wish to be named.

The cemetery is also where Anatoly Onoprienko, the so-called “Beast of Ukraine,” who admitted to the murders of 52 people, was laid to rest following his death in 2013.

Onoprienko and Tkach were cell block mates until the death of the former, who also died from heart failure.

6 Sergey Tkach pictured with his wife Elena Credit: Netflix

Tkach and his wife, Elena, at 26, four decades younger than him, were interviewed earlier this year as part of a Netflix series "World’s Toughest Prisons" which followed day-to-day life in the Zhytomyr penitentiary.

The documentary is presented by ­journalist Raphael Rowe, who was freed after serving 12 years in a British jail for a murder following the quashing of his conviction by the Court of Appeal, reported Mirror.

In the programme, Mrs Tkach said that she wrote dozens of letters to the serial killer when she saw him being interviewed following his arrest after he murdered a nine-year-old girl near in the central Zaporizhia region.

She said: “(I was drawn to) his manners, I guess, some sort of magnetism.”

6 Tkach died from heart failure in Zhytomyr, Ukraine

6 Journalist Raphael Rowe, who presented the Netflix documentary 'World's Toughest Prisons' Credit: Netflix

“I wrote, truthfully, that I saw his interview, and wanted to communicate, to have a conversation.

“And just too get to know him better.”

When asked about Elena’s first conjugal visit to Zhytomyr colony, Tkach said: “Every hour, (the guards) came and checked. Everything is fine, everything is OK."

“Today we can sit together, hug and kiss freely.”

Before agreeing to the interview, Mrs Tkach insisted that no other women could be present whilst filming, because she believed that her husband "was irresistible.”

In the programme, she said: “I do not believe in the total number of cases. I believe it was a lot less. Secondly, it does not matter that much to me.”

Mrs Tkach, a Russian national, gave birth to the couple’s only child in 2016 but was forbidden from the bringing the girl to visit Zhytomyr prison.

6 Tkach speaks to Rowe during the Netflic documentary 'World’s Toughest Prisons' Credit: Netflix

6 Tkach pictured during his time as a police officer Credit: Wikipedia

Criminals similar to Sergey Tkach would usually be held in cages, however Ukrainian's laws mean all married prisoners are allowed a three-day conjugal visit every two months.

At the time of the interview, Tkach, who blamed alcoholism for his atrocities, said that that his only motivation to keep living was “for the love of my daughter and my wife.”

The Zhytomyr prison official told The Sun Online: “Tkach’s wife has not visited him since the summer and we believe that he died of a broken heart.”

Earlier this year, Elena deleted her VK social media account, after posting: “The secret world government, the Illuminati and the Zionists are hunting for my personal data. I’m going underground.”

Tkach was a Soviet police detective before commencing his quarter-century killing spree.

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He had previously told Ukrainian television reporters that he wanted to better the murder totals of other notorious serial killers.

He typically raped his victims, all women aged 9 to 17, before or after he strangled them to death.

At least three innocent men were convicted of crimes Tkach committed, including one who killed himself in custody, after being accused of murdering his own daughter.