Tragic Hayley Stringer, 29, was killed by husband David, 32, while their three young daughters were asleep upstairs at the home in Walsall.
Her estranged husband then committed suicide by stabbing himself with the same kitchen knife.
The couple, who had been together for 11 years and married for 10 years, separated around March 29 this year.
An inquest heard that around the same time as they split up, factory worker Hayley started a relationship with 19-year-old Matthew Read.
Sandwell Coroners Court heard David returned to the family home in Hollemeadow Avenue, Blakenall, where Hayley had remained with their children in the early hours of May 10.
The pair argued before David stabbed her repeatedly before killing himself.
The couple's bodies were discovered hours later by Mr Read who returned to the house at 3.50am after finishing a night-shift at work.
Detective Constable John Brindley, from West Midlands Police, told the hearing at Smethwick Council House: "The two persons had been in a relationship for about 11 years, married for about 10 years and had two children in that period aged eight and seven.
"Hayley had a further child aged 11 from a previous relationship.
Hollemeadow Avenue, where the tragedy happened
"The relationship between Hayley and David came to an end around March 29 this year. We know that Hayley commenced a relationship with another man around that time.
"It would appear that they (Hayley and David) weren't getting on and decided to split.
"It was just prior to 3.50am on May 10, a call was received to ambulance control from a distressed person, Matthew Read.
"He said that the husband had come back and stabbed Hayley.
"When asked who he meant, he said David Stringer who was also there and had a knife present in his own body.
"The police attended the scene where they found exactly what Mr Read had said.
"He (Mr Read) was actually at work and had made arrangements to arrive when he had finished his shift.
"The first officer there noticed the front door open, Mr Read was standing in the hallway.
"There was blood on the door and a female later identified as Hayley had numerous injuries and appeared deceased on the floor.
"A male later identified as David also appeared deceased within the lounge and hallway in a sitting position against a wall.
"Obviously there were children within the premises that were taken to a neighbour.
"The children were asleep upstairs and were carried asleep from the residence to the neighbours."
The inquest heard the couple, who were discovered in the hallway and lounge of the house, were both pronounced dead at the scene by paramedics.
Hayley's cause of death was given as multiple stab wounds which caused blood loss, a
collapsed lung and an obstruction of her airway.
Her husband, who was discovered in a sitting position against a wall with the knife still in his body, died from a single stab wound to the chest.
Detective Constable Brindley told the hearing David had previous made threats to kill Mr Read and take his own life but said these had not been reported to police.
He added: "Enquiries were made with both families and a set of knives was recovered from David's father's address.
"One knife was missing from that set. It was the knife that was recovered at the scene that was still present within David.
"It was a Swiss type kitchen knife, a carving knife.
"There were certain references to threats being made, threats to kill being made against Mr Read and David threatening to take his own life as well.
"No complaints were made to the police, they weren't notified of this. That only came to light once the examinations of various mobile phones and computers was conducted.
"From all the evidence and statements that have come to light during this investigation, the conclusion is that David attacked his wife using a large knife from a collection which was at his father's house following which he took his own life."
The inquest heard Mr Read was arrested at the scene and initially treated as a suspect until he was later ruled out after officers checked with his workplace.
Dc Brindley said: "Because of the circumstances of what the officers found, they found it necessary to arrest Mr Read.
"Enquiries were made with his work and he was captured on CCTV leaving his work. He would then have to ride his bike from Cannock to Walsall.
"The timings for the journey all fit into line. He was eliminated from the inquiry."
Black Country Coroner Zafar Siddique concluded that Hayley was unlawfully killed before ruling that David committed suicide.
He said: "We heard in evidence that Hayley Stringer and David Stringer were in a long-term relationship, they had a number of children.
"For a number of reasons which isn't clear they decided to end that relationship at the end of March this year. From the evidence Hayley then went on to form a new relationship with a Mr Read.
"On the day of the incident, a call was received from Mr Read that when he arrived home he had seen Hayley and David with significant injuries and stab wounds.
"What has unfolded then was that clearly an argument or altercation had taken place between the two parties whereby David had stabbed Hayley.
"She ultimately died from a number of multiple stab wounds and the cause of death was multiple stab wounds.
"David had received one single stab wound to the chest and the cause of death was a stab wound to the chest.
"Having considered all the various evidence my conclusion in relation to Hayley is that she was unlawfully killed.
"In respect of David I'm satisfied that he took his own life and therefore he committed suicide.
"This is a double tragedy for both families involved, particularly the children involved, and my heart and sincere condolences go out to both sets of families."