He wasn’t able to accept the breakup and stabbed Janet Scott on a street on the outskirts of Nottingham before driving her to the city centre.
Mrs Scott did manage to escape from the car and flag down a traffic officer. But as the pair waited for help, Mellors drove the car straight at them - killing her and severely injuring the traffic officer.
Mellors was charged with murder but shortly after, took his own life at Manchester Prison before he was able to stand trial.
He had previously beaten and strangled to death his then partner Pearl Black, at their home in Bramcote in 1999, but had been released back into the community on licence.
So why was Simon Mellors free to kill again?
When someone serving a life sentence is released on licence they can be recalled to prison at any time if they break the conditions of their licence.
Simon Mellors was supposed to divulge his past conviction to any future partners and any worrying behaviour could have meant a recall to prison.
The inquest heard how Mellors had breached his conditions a number of times.
However, no warnings, sanctions, or calls to the police were made by his probation officer Andrew Victor.
Lack of response
Mellors had been following Janet Scott and waiting outside her place of work.
The inquest heard that she had contacted the probation service and made them aware of Mellors’ behaviour, which was similar to the events which led to him committing his first murder.
The probation service should have triggered a multi-agency response. This, the inquest heard, would have brought in the police service and could have seen Mellors recalled to prison.
But this did not happen, as his probation officer Andrew Victor never acted on the concerning information he received from Mrs Scott.
The offender manager during the critical period placed insufficient weight on the information given to him by Janet about Simon Mellors' stalking behaviour. He failed to identify the behaviours of being of concern.
Coroner Jonathan Straw said Mr Victor was working with a case load "significantly higher than it should have been" and he had complained to bosses that he was "overwhelmed and stressed."
He said this would have impacted on the quality of his decision making but the coroner added: "I am not of the view that work pressures affected or contributed to the failure of (Mr Victor) to escalate risk during the critical period.
"It undoubtedly impacted to a degree on early decisions and assessments."
Probation officer Andrew Victor told the hearing that at the time, he saw Mellors' behaviour as 'harassment'. But now that he'd had training, he recognised it as stalking.