Ian Stewart found guilty of murdering wife in 2010, six years before he killed his author fiancee Helen Bailey

A 61-year-old man will spend the rest of his life in prison after being found guilty of murdering his wife in 2010, six years before he went on to kill his fiancee at their home in Hertfordshire.

Ian Stewart denied killing Diane Stewart who died at their family home in Bassingbourn, Cambridgeshire, on 25 June 2010.

The 47-year-old's cause of death was recorded at the time as Sudden Death in Epilepsy (Sudep).

Stewart will die behind bars after he was sentenced to a whole-life order on Wednesday.

He told his trial at Huntingdon Crown Court that he found his wife collapsed in the garden when he returned from the supermarket.

He said he tried to revive her, attempted to contact neighbours who were a doctor and nurse, tried again to revive his wife, and then called 999.

Her death was not treated as suspicious at the time and although a post-mortem was carried out, it was not a forensic post-mortem.

Case re-opened after fiance's murder

Police reopened the case after Stewart, 61, was convicted six years later of the murder of his fiancee, children's book author Helen Bailey, whose body was found in the cesspit of the £1.5m home they shared in Royston in Hertfordshire.

Stewart was found guilty of Ms Bailey's murder at St Albans Crown Court in 2017 and was handed a life prison sentence, with a minimum term of 34 years before he could be considered for parole.

He had spent weeks poisoning Ms Bailey with prescription sedatives before smothering her and dumping her body, where it lay undiscovered for three months alongside the body of her dog, Boris.

He stood to gain £1.8m in investments - plus the value of two properties.

As part of the police investigation following Stewart's 2017 murder conviction, consultant neuropathologist Professor Safa Al-Sarraj was asked to examine preserved parts of Mrs Stewart's brain, which had been donated to medical science.

Read more: The children's author killed by the man she loved

Evidence she had been suffocated

Prof Al-Sarraj said there was evidence that Mrs Stewart's brain had suffered a lack of oxygen prior to her death, and he estimated that this happened over a period of 35 minutes to an hour.

Prosecutor Stuart Trimmer QC said Mrs Stewart's death was "most likely caused by a prolonged restriction to her breathing from an outside source", such as smothering or a neck hold.

Although Stewart said he believed his wife had an epileptic fit, she had not had one for 18 years and took daily medication. Consultant neurologist Dr Christopher Derry estimated that her risk of having a fatal epileptic seizure was about one in 100,000.

The court heard that Stewart received £96,607.37 after his wife's death, in the form of £28,500.21 from a life insurance policy and the rest from bank accounts.

He denied the murder of his wife, and during the trial at Huntingdon Crown Court he described his conviction for the murder of Ms Bailey as a "miscarriage of justice".

Sons were out that day

The defendant looked across from the secure dock to his two sons who sat in the public gallery after the unanimous verdict was returned.

Both of the couple's sons were out on the day of their mother's death, with then 15-year-old Oliver at school and Jamie, then 18, taking his driving test.

Jamie Stewart had told the court that he recalled "raised voices… between my mother and father" when he was at home on study leave for A-Levels the week his mother died.

'Greatly loved'

Diane's family paid tribute to her, calling her a "very special, caring and capable person".

Wendy Bellamy-Lee, Diane's sister and brother Christopher Lem said: "She will always be greatly loved and hugely missed by her family and all who knew her. We have many happy memories of growing up together through the years and later having close bonds sharing our family lives together. Tragically she died far too soon, she will always be in our hearts."

Her sons, Jamie and Oliver Stewart said: "Our Mum was amazing. All the people we have spoken to and things we have heard since her death have only enhanced this feeling. We were privileged to have a wonderful caring upbringing and we were supported through all the activities and hobbies that we undertook.

"It's been really upsetting the last six years to have to recall the events of the toughest time of our life. We now look forward to recalling the many happy moments we had growing up as a family. At this extremely difficult time, we wish for our privacy to be respected."