Ex-lover of identical twin allegedly murdered by her sister gives insight into their "toxic" relationship.

The eerie case of identical twin yoga instructors, Alexandria and Anastasia Duval, has taken yet another mysterious turn.

Two weeks after Alexandria’s murder charges were reinstated for the unusual death of her sister – who lost her life when the pair’s SUV, driven by Alexandria, went off a cliff in Hawaii in May this year – her sister’s former boyfriend has provided a chilling insight into the “toxic” relationship the pair shared.

Eyewitness accounts that Alexandria purposefully killed her sister is not a far fetched one, Keith Weiss says.

Weiss, a chef from Florida, dated Anastasia some ten years ago when she went by the name Ann and Alexandria by the name Alison, and still remembers the "intense fighting" the twins regularly engaged in.

He also recalls at least two occasions where the pair became physically violent while driving.

“The first time, Ann was driving, and they just started fighting,” Weiss told People.

“She let go of the wheel and they were going back and forth with each other, oblivious to the obvious danger and the other cars around us. She almost lost control of the car.”

During the second episode of outrage, things escalated to such a degree that he was compelled to end his six-month relationship with Anastasia.

“We were driving home and they wanted me to stop so they could get some wine,” he explained. “But I didn’t want to stop, and Ann, she started kicking my hands … kicking them off of the steering wheel. Alison (now known as Alexandria) was kicking the windows and they were screaming, ‘I want you to stop!’ I told them, ‘You’re going to end up killing us’.

“They didn’t care.”

The aggression and ferocity didn't end there, either. A disturbing argument in the middle of a shopping also raised red flags for Weiss.

"I remember this one time, the three of us were at the mall, and Ann smacked Alison in the back of the head. Hard. They raged. They went back and forth with each other, pulling hair, pinching each other … it was as if they had blocked everything out around them.”

Alcohol was often the precursor to the drama, Weiss told the publication.

“[After they had been drinking] I once got call from Ann saying, ‘Get over here now … I’m going to kill her'. She actually started hitting Alison with the phone. I heard it … thump, thump, thump. They were both screaming at each other.

“I get to their apartment and there’s broken glass everywhere from wine bottles and shattered glasses. There was blood everywhere, and the bedroom door was falling off its hinges.

"I asked them if they were okay, and they were like, ‘We’re good, we’re fine. We’re just watching a movie.’ Meanwhile, all around them it’s total destruction. They seemed to not know they wanted to kill each other just minutes earlier.”

While Alexandria was originally cleared by a judge of Anastasia's murder, new and unspecified evidence emerged last month, prompting the refiling of the second degree murder charges.

Shortly after, authorities arrested Alexandria in New York. She will next appear in a Hawaiian court on December 16.

On her behalf, public defender Terence Kindlon said: "She is very distraught. Very distraught. And I think that if nothing else she needs just to reach a greater state of peace with herself because this has been a terrible experience with her. Her sister was her soul mate."

Before infamy, the sisters lived controversial lives of failed business ventures, personal bankruptcies, fraud and mystery.