Harry Jarvis hid his mistress in his garden shed before murdering his spouse, Carol, and leaving her decaying body in the cellar in 2009.
His lover, Jus-Rol pastry heiress Rita Heyster, who was living in the garden hut, helped him to conceal the body at his home at Balbardie Crescent, Bathgate, West Lothian.
Jarvis, 67, was found dead in his cell at Addiewell Prison in West Lothian in April last year and a fatal accident inquiry into the circumstances was held at Livingston Sheriff Court earlier this year.
The probe was told Jarvis had complained of feeling unwell and had been taken to see medical staff by a prison officer.
But he collapsed soon after he was returned to his cell and efforts to revive him failed.
He was rushed to St John’s Hospital in Livingston but was pronounced dead soon after.
Sheriff Peter Hammond has ruled Jarvis suffered a fatal blood clot in the heart and nothing could have been done to save him.
Jarvis was jailed for a minimum of 15 years in 2011.
Him and Heyster were charged with murder after mother-of-four Carol’s body was discovered. Her remains were found taped up in a duvet in the basement of the house after she was reported missing by her children.
They did not believe their father’s account that their mother had taken a trip to Dundee or gone into care.
Heyster, from Coldstream in the Borders, inherited a £2.5million fortune from her adoptive father, Jus-Rol founder Tommy Forsyth.
But she fell on hard times and squandered the cash before meeting Jarvis.
Their first contact in May 2008 was through the internet and, later, he stayed at her Peebles home because he was working in the area as an electronics engineer and moonlighting as a delivery man for an Indian take-away.
The following year Ms Heyster moved to the Bathgate area, living in bed and breakfast accommodation and, for about a month before his wife’s death, staying “odd nights” in the garden shed.
She was jailed for four-and-a-half years for helping to conceal Carol’s body.
In 2015, the pair planned to marry behind bars but Heyster called off the wedding.
Sheriff Hammond concluded: “There were no suspicious circumstances.
“There was no basis for suggesting that anything could or should have been done differently so as to prevent Mr Jarvis’s death.
“He was seen promptly when he asked for help and did not appear unwell until he collapsed.
“He was not flushed, pallid, clammy or distressed. Clinical readings were normal and he was appropriately referred
for a second opinion.”
He added: “From all of the evidence presented at the Inquiry I conclude that Mr Jarvis’s death was an unpreventable one due to natural causes and I have no recommendations to make.”