A woman who claims to have had an affair with Chris Watts said she met him on Tinder and on their first date they watched a movie believed to have inspired the Colorado killer's lies.

Before Watts killed his pregnant wife Shanann, their two daughters Bella, four, Celeste, three, and their unborn son Nico, he was known as a 'funny' and 'charming' guy to Amanda McMahon.

McMahon told Inside Edition that she met Watts on the dating site last March.

He told her that he was divorced. On their first date they grabbed tacos and watched Shutter Island, which stars Leonardo DiCaprio.

Amanda McMahon (left) who claims she had an affair with Chris Watts (right) said she met him on Tinder and on their first date they watched Shutter Island, a movie that may have inspired the Colorado killer's lies

Though McMahon said Watts 'seemed like a genuine guy,' it has been speculated that some of his lies were inspired by the movie. In Shutter Island DiCaprio (pictured) plays a husband who murders his wife in a rage after she kills their children, which is one of the lies Watts told police

McMahon said her relationship with Watts was short-lived after she found out he started seeing his co-worker, Nichol Kessinger (pictured with Watts)

Though McMahon said Watts 'seemed like a genuine guy,' it has been speculated that some of his lies were inspired by the movie.

In Shutter Island DiCaprio plays a husband who murders his wife in a rage after she kills their children, which is one of the lies Watts told authorities when he was questioned over his family's murders.

Watts told agents a similar story, claiming that Shanann choked the girls to death and he killed her after witnessing the act.

'The evil that I saw when I walked behind Shanann when she was [choking daughter Celeste],' Watts told detectives.

'I didn't know what to do. I didn't know what to (expletive) do. None of this made sense!' he said.

McMahon said her relationship with Watts was short-lived after she found out he started seeing his co-worker, Nichol Kessinger.

'He seemed like a genuine guy,' McMahon told Inside Edition.

But she said that all of that changed after their first sexual encounter, which involved 'rough sex'.

On the night before Shanann's (left) death she lined up the child care for the weekend. At the same time, Watts (right, recent mugshot) was with his mistress Kessinger discussing his next steps and the apartment he planned to get when he separated from his wife

Watts had taken the girls (pictured) to a birthday party on the afternoon of Sunday, August 12, and while Bella and Celeste played in the pool their father started texting co-worker Kodi Roberts

Watts confessed to all three murders to avoid the death penalty and was sentenced to five life sentences in late November

'The best way I can describe it that he almost zoned out into a different person,' she told the news site, adding that when he placed his hand around her neck, she 'freaked' out.

McMahon described him as being 'very forceful'.

She also told the news outlet that she would have never engaged with Watts had she known he had a wife and two children at home.

'He was married, he had a wife at home, pregnant, two daughters at home,' said McMahon. 'I know how that hurts. I wouldn't do that to her.'

On the night before Shanann's death she lined up the child care for the weekend.

At the same time, Watts was with his mistress Kessinger discussing his next steps and the apartment he planned to get when he separated from his wife.

He had told Shanann he was at a baseball game, but her suspicions had grown so strong that she told friends of her plan to confront her husband when she returned from her work trip in Arizona.

Watts had taken the girls to a birthday party on the afternoon of Sunday, August 12, and while Bella and Celeste played in the pool their father started texting co-worker Kodi Roberts.

At 5.06pm that evening, Watts set in motion his plan for disposing of his wife and daughters' bodies, as he texted Roberts that he would be making the drive out to one of the more distant oil fields that was managed by his company, Anadarko Petroleum Corporation

Watts, per his own admission in interviews with law enforcement officials, then took his daughters (pictured) home, gave them both showers, fed them pizza and got them each a snack before putting them to bed

Hours later, the girls and their mother Shannan were all murdered in the house, and their bodies disposed of at Cervi 6-29, an Anadarko oil field

At 5.06pm that evening, Watts set in motion his plan for disposing of his wife and daughters' bodies, as he texted Roberts that he would be making the drive out to one of the more distant oil fields that was managed by his company, Anadarko Petroleum Corporation.

It is also where the bodies of Shanann, Bella and Celeste were discovered just days after they went missing.

Watts, per his own admission in interviews with law enforcement officials, then took his daughters home, gave them both showers, fed them pizza and got them each a snack before putting them to bed.

He noted that both girls were eager to see their mother, who was due to return home late that night.

Hours later, the girls and their mother Shannan were all murdered in the house, and their bodies disposed of at Cervi 6-29, an Anadarko oil field.

Watts confessed to all three murders to avoid the death penalty and was sentenced to five life sentences in late November.