The predatory partner of Helen Bailey has been found guilty of drugging and killing the children's author in a long-planned plot to acquire her riches.
Driven by greed, Ian Stewart secretly spent months poisoning the Electra Brown writer with his sedatives, smothering her once she had been stupefied in April last year.
The lifeless 51-year-old was dragged into a foul cesspit hidden deep below their luxury Hertfordshire home, where her body lay undiscovered for three months.
Following a six-week trial at St Albans Crown Court, a jury of five women and seven men found Stewart, 56, of Baldock Road, Royston, Hertfordshire, guilty of murder, fraud, three counts of perverting the course of justice and preventing a lawful burial.
Police said the "sudden, unexpected" death of Stewart's first wife, Diane - who was found in the couple's garden in 2010 - will now be re-examined.
Stewart scoped out the vulnerable widow on the internet in 2011 - earning his way into her trust and later her £3.3 million estate after launching a "love-bombing" offensive.
"She was being grossly deceived by someone who was preying on her," prosecutor Stuart Trimmer told his trial.
Over many weeks, Stewart surreptitiously fed Ms Bailey his prescription anti-insomnia drug, Zopiclone, possibly by slipping it into her morning scrambled eggs.
She soon became panicked by her deteriorating state of mind, searching online for terms such as "can't stop falling asleep" and expressing concern to loved ones.
A pillowcase found next to the author's body led the prosecution to suggest Stewart used a pillow to smother her while she was sedated.
Ms Bailey, known for her young adult stories and memoir on bereavement, was finally found submerged in a tank of human sewage underneath the couple's garage on July 15 last year.
Dead at her side was Boris the dog, her loyal companion.