Austin Harrouff, a 19-year-old FSU student, is accused of murdering married couple John Stevens and Michelle Mishcon as they sat in the garage of their Tequesta, Florida home. The 19-year-old was dubbed the “cannibal killer” by the media after he allegedly stabbed the couple to death, biting one of his alleged victim’s face and abdomen while making animal noises, and then stabbing the couple’s neighbor who was attempting to save their lives.

WATCH: Father Of Frat Boy Dubbed 'The Cannibal Killer' Describes What He Calls Son’s ‘Abnormal’ Behavior Before The Attack

The violent crime and Austin’s reportedly superhuman strength left police questioning if the “zombie” street drug Flakka was to blame. But Austin’s father, Dr. Wade Harrouff, says he believes mental illness caused the tragedy.

WATCH: First Thing Police Reportedly Told Father of Teen Who Allegedly Committed Gruesome Murders: ‘He’s Killed Two People And Eaten Them’ 

In an exclusive sit-down interview with Dr. Phil airing Wednesday, Dr. Harrouff apologizes for his son’s behavior and shares a message with the victims’ families.

“It’s just the worst thing I could ever think of. This is the biggest nightmare I could ever even dream of,” Dr. Harrouff says. “I’m deeply sorry for what my son did to those people. And I apologize for him, because my son would have never done that. He’s such a good person.”

WATCH: The One Thing Dad Of Florida Frat Boy Accused Of Gruesome Murders Wants People To Know About His Son

This episode of Dr. Phil airs Wednesday. Watch more here.