An Arizona mother who shot her two sons in a murder-suicide 'lost her mind' after finding out her husband had been cheating with a co-worker, according to a friend.

Andrea Clarice Davis, 38, is believed to have killed her children, aged 10 and 18 months, at a home in Phoenix, after first attacking a woman her husband was with. 

Police said she started her rampage just after midnight on Monday at Tailgaters Sports Bar & Grill in Glendale, where her husband was drinking with a 36-year-old woman. 

Glendale Police said the husband, Nolan Davis, 39, called 911 and told officers his wife had fired shots at the back of the woman's head as she tried to leave the parking lot outside the bar.  

The victim, who has not been identified, was treated in hospital for non-life-threatening injuries, and she is expected to survive. 

Police did not confirm the relationship between Nolan Davis and the victim, but Andrea's friend, Amy Bowers, said she was his alleged mistress. 

Bowers said Andrea and Nolan Davis had a blissful marriage at first after being together for more than 12 years - but this fell apart when Nolan began having an affair with a co-worker. 

'This relationship that's been going on between Nolan Davis and his co-worker has completely made her lose her mind,' Bowers told Arizona Family. 

'She hasn't had an issue like this their whole marriage. They haven't had anything like this come up before. And so I think the shock of that is just a lot for her. 

'She was just, she was not feeling good. And she's been asking for help from everybody. Like it's not been secret.'

Bowers said the boys - Austin, 10, and Andolan, 18 months - were 'really great kids'.  

'Andolan is so sweet and she has one of the most beautiful eyes,' she said. 

'And Austin, he loves coming and hanging out at my house and playing Mario Party. I painted his whole bedroom. It's all Mario-themed.'

'I feel really bad nobody was thinking about the kids this whole time you know Andrea was stressed because Nolan was talking about leaving and she was like, "What am I supposed to do with the kids?"' Bowers added. 

In a Facebook post immediately after the shooting, Nolan said: 'Andrea just attempted murder on me. Tried shooting me in the face and tried shooting my unfriend [sic] in the car.'

Felicia Queen, a cousin of the children's father, told AZ Family that the high school sweethearts had been in the process of separating, adding that Andrea knew 'a lot about guns'.

Queen said that her cousin was a huge gun advocate with a concealed weapons permit who would have taught his wife 'how to protect herself and the kids if anything ever happened'.

'Don't portray her as an evil person. It's not ok what she did but she wasn't a horrible person, she was a good mom,' Queen added to Fox 10 Phoenix.

For about four or five years, Andrea worked a 'really good job' while Nolan was a stay at home dad looking after their eldest son.

'That would be the hardest thing for him right now because they were best friends. They were little buddies,' Queen said.

Queen launched a fundraiser to help support Nolan and cover the children's funeral expenses. The family asked for privacy.

Police said Nolan dialed 911 around midnight at the start of his wife's bloody rampage, saying she had shot a woman in the head in the Tailgaters Sports Bar & Grill parking lot. 

Nolan also told cops his wife texted him as she fled in a gray SUV to a home in Phoenix, around two miles from the bar, saying she was going to hurt their children. 

Minutes later, he received a haunting photograph from Andrea, showing one of their children bleeding from the head. 

'The male victim subsequently received a text message containing a photo of one of the children bleeding,' Glendale Police told the Daily Mail in a statement. 

Glendale and Phoenix police officers said they rushed to the home, arriving at about 2.30am, but it was too late to save the boys. 

Officers were confronted with a grisly scene, as Andrea and both her sons lay dead. 

'It is very difficult to deal with today,' Phoenix Police Sergeant Lorraine Fernandez told AZ Central. 'No one wants to see harm done to children.' 

According to ABC 15, no record of prior domestic violence reports had been made in the area.

Both scenes remain active, with the Glendale Police Department investigating the bar scene and the homicide investigation under the control of the Phoenix Police Department. 

The Daily Mail has reached out to the Phoenix Police Department for comment.