The Yorkshire Ripper reportedly threatened Ronnie Kray after the gangster "made advances" toward the serial killer in Broadmoor.
Convicted murderer Peter Sutcliffe, who murdered 13 women in a six-year killing spree, was convicted in 1981 and spent three decades at the high-security psychiatric hospital before being moved to HMP Frankland in 2016.
Sutcliffe described how Kray tried to flirt with him in a letter to a friend six months before his death.
The pair were both held at high-security psychiatric hospital Broadmoor in the early 1990s.
Kray and his twin brother Reggie committed murder, armed robbery, arson and ran protection rackets while mixing with big name celebs in the 1960s.
Ronnie Kray died, aged 61, in 1995, while Sutcliffe died at HMP Frankland from a combination of Covid-19 and heart disease in November 2020, aged 74.
Before his death, Sutcliffe wrote a number of letters, reports The Sun.
In one letter, he wrote: “I did not give Ronnie a beating although I did threaten him when he tried to make advances on me.”
In another, he spoke of his mum: “My mum died of a massive heart attack on 8th November 1978 before my arrest, so she never knew about my mission etc!”
The Yorkshire Ripper was kept in chains until shortly before his death and not allowed to call his wife, an ombudsman report revealed earlier this year.
The serial killer, who was blind and used a wheelchair, had refused hospital treatment, the report said.
Sutcliffe’s killing spree began in October 1975 with 28-year-old mother-of-four Wilma McCann, who was hit with a hammer and stabbed 15 times.
He was interviewed nine times during the course of a huge investigation but continued to avoid arrest and was able to carry on killing.
Over the next five years, the Ripper claimed the lives of 12 more innocent women before finally being apprehended by police in Sheffield for driving with false number plates and convicted in 1981.