High-profile vegan chef and author killed his son, 10-month-old daughter, and wife' 90 minutes after he posted their Christmas photos (Details, pics)

The man thought to have killed his estranged wife and two children on Christmas is a well-known vegan chef, author and motivational speaker who suffered from depression but recently turned his life around.

Police said Tuesday that Anthony Milan Ross was arrested late Monday night after exchanging gunfire with officers following a six-hour standoff in a Phoenix, Arizona apartment complex, according to AZ Central. The 45-year-old has been charged with three counts of first-degree murder and more than a dozen counts of aggravated assault on an officer. He wasn't hurt in the police standoff.

Witnesses told police they saw him shoot his estranged wife Iris Ross as she tried to run away from him. Then when they asked if she was fine, he said 'no' and pointed his gun at them before entering his apartment, where witnesses said they heard two or three more gunshots, according to police.

On Christmas afternoon Ross posted a touching video alongside his 11-year-old son, Nigel, singing 'Santa Claus is Coming to Town.' Just 90 minutes later police said the shooting rampage began.

Ross's social media fans have reacted with shock by the disturbing news, as hundreds of his fans commented their horror on the video, which remains on his page.

Police responded to the apartment at around 4pm on Monday afternoon, finding Iris's body outside an apartment in the complex. When police began to enter the apartment a standoff with Ross ensued.

Ross, who was commonly known by Milan by his fans, lost a significant amount of weight in his 20s when he switched to a vegan lifestyle. He then became a chef and started writing and doing inspirational videos about his transformation and new lifestyle.

Ross was also featured alongside celebrities such as James Cameron and Samuel L Jackson in a feature-length documentary about veganism.

His Facebook profile more than 6,200 followers as of Tuesday night, though it seems that number may have dwindled throughout the day as news of the tragedy spread. However, Ross was also battling depression, according to Iris's sister Mary Wogas.

'I received a text yesterday around 2.52pm,' Wogas told ABC 15, explaining that the texts came from her former brother-in-law.

'Two messages, first one saying "I just killed Iris and the kids. The second message was "with a gun." I knew that man was very unstable. I knew he had a very, very dark side. I didn't know it was this dark.'

Tuesday morning police confirmed Ross as the father of the two dead children and that he and Iris were an estranged couple.

After finding Iris's body and confronting Ross, they negotiated with him for hours in a standoff, hoping that one or both of them were still alive. He eventually told them that he'd killed the children, according to Sgt. Jonathan Howard, but not until after he'd changed his stories and said they were alive and threatened to kill them if police didn't leave him.

After several hours the Special Assignments Unit sent a robot into the apartment and it became apparent that the infant, Anora, was dead.

'Throughout the negotiations, he made comments that he had killed the children. He made some notifications to some family members that he had killed the children,' Howard said.