Stephen Beadman died on Thursday while serving a life sentence for the rape and murder of the Leicestershire teenager.
Beadman was jailed in 2016 for a minimum of 35 years over the horrific crime which took place the year before.
Miss Haywood, from Measham, was brought to another man Luke Harlow's flat in Ibstock, Leicestershire, where Beadman attacked her. Her body was discovered in a nearby field three days later, following a police search involving 300 officers.
Beadman, then 29, later pleaded guilty to murdering Kayleigh while Harlow, who had groomed the teenager online, was also jailed for 12 years for his involvement in the crime.
When both men were jailed in July 2016, the judge described Facebook, WhatsApp and text messages sent by Harlow to Kayleigh and other girls as “chilling”.
During the hearing, Harlow’s barrister described Beadman, whose computers contained child abuse images and extreme pornography, as “the monster that lived next door”.
A Prison Service spokesman this morning confirmed the death of 34-year-old Beadman, who was being held at HMP Wakefield in West Yorkshire.
Beadman died on Thursday, but the cause of his death has not been confirmed.
The Prison Service spokesman said: “HMP Wakefield prisoner Stephen Beadman died in hospital on April 8. The Prisons and Probation Ombudsman has been informed.”
Support The Yorkshire Post and become a subscriber today. Your subscription will help us to continue to bring quality news to the people of Yorkshire. In return, you'll see fewer ads on site, get free access to our app and receive exclusive members-only offers. Click here to subscribe.