A father killed himself and his three children after his relationship with his wife broke down after she developed a crush on her lecturer, an inquest heard.
Ceri Fuller, 35, is believed to have stabbed his 12-year-old son Samuel and daughters Rebecca, eight and Charlotte, seven, with a hunting knife, before killing himself.
All four bodies were found at the bottom of a disused quarry in Shrewsbury, Shropshire, on July 16 last year.
The children had been slashed in the neck, and Samuel and Rebecca are believed to have tried to defend themselves.
An inquest into their deaths heard his wife, Ruth Fuller, told her sister Joanna Ballard that she and her husband had agreed to split up before he disappeared with their three children from their home in Milkwall, Gloucestershire, and that he had 'understood' the split.
Mrs Fuller, 34, also admitted to having a 'schoolgirl' crush on her Open University lecturer Mark Lindley-Highfield, and had posted a message on Facebook days before the bodies were found referring to a 'bonkers midlife crisis'.
The inquest heard that after Mrs Fuller was taken into hospital before the bodies were found she told her sister: "I think that Ceri killed Rebecca."
Mrs Ballard said her sister had admitted a small crush on Mr Lindley-Highfield, but said this was just a 'schoolgirl' crush and she had no plans to take it further.
The children and their father were reported missing on July 12 last year after he had failed to turn up for work at a paper mill and the children had not been seen at school.
Their bodies were found four days later at Poles Coppice in Pontesbury Hill, near Shrewsbury.
The inquest heard Mrs Ballard had been called to her sister's home at about 6.30pm on July 12 and had been told she had tried to kill herself.
She said when she arrived no one knew where Mr Fuller and the three children were.
She said: "I looked through Ruth's phone and saw only loving texts between Ruth and Ceri even into Wednesday morning.
"I saw a text from her to Mark, her university lecturer, asking him out for a drink and another saying it was meant for Ceri.
"Ruth had told me she had a crush on Mark before. But she saw it as a schoolgirl crush and wasn't taking it further.
"Before we went to hospital I asked her where Ceri and the children were and where but she just looked at me blankly and said 'mmm-hmmm'."
Mrs Fuller was taken to hospital in Gloucester at about 10.30pm where she told her sister that she and her husband were splitting up and that he 'understood'.
But in the early hours of July 13 Mrs Ballard said her sister looked into her eyes and told her: "I think that Ceri killed Rebecca."
Mrs Ballard told the court that there was nothing to suggest her sister had started a relationship with her humanities lecturer.
She described the pair as a loving couple but said Mr Fuller could be possessive.
Deputy coroner for Mid-Shropshire Andrew Barkley asked Mrs Ballard if Mr Fuller had been 'unnaturally possessive' towards his wife.
She said: "In my opinion yes, it was more possessive than I would be comfortable with in a relationship.
"It seemed to me that he seemed uncomfortable with Ruth wanting anything that wasn't being a mum."
The inquest heard Mrs Fuller and Mr Lindley-Highfield exchanged a string of text messages between July 11 and 12 last year.
In one of the messages Mrs Fuller referred to a mid-life crisis and Mr Lindley-Highfield responded reminding her of the boundaries between a tutor and student.
Mrs Fuller had started a humanities course in January last year, which included tutoring sessions with Mr Lindley-Highfield held at Cheltenham College.
The inquest concluded that the children were unlawfully killed by their father.
The coroner Andrew Barkley said "What exactly happened on that fateful day might never be known but it became a scene of unimaginable horror and the stuff nightmares are made of."Moving open letter from the grandfather of three children killed in the woods