Ex-boyfriend of 'yoga twin' speaks of sisters' violent tempers: From 'Jekyll to Hyde'

There are new details in the troubled relationship between twin sisters that allegedly ended in murder.

Keith Weiss, who once dated slain sister Anastasia Duvall, told Inside Edition Wednesday that the twins often fought, and the altercations often turned physical.

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"I knew something was going to happen," he said. "I knew it was just a matter of time – just never thought it would unfold like a made-for-TV kind of movie."

Weiss said Anastasia called him one night, saying she was going to kill her sister. "I'm like, 'wait, what's going on?' And she's like 'Alexandria and I are fighting.'

"And all of a sudden I hear thump, thump, thump. And she's like, 'That's me. I'm hitting her with the phone.'"

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Alexandria is charged with murdering her sister by intentionally plunging their car off a steep cliff in Maui. Anastasia died from her injuries, while Alexandria was critically hurt and has since recovered.

She is being held without bail in upstate New York, where she is awaiting extradition to Hawaii.

Witnesses to the crash said the women appeared to be arguing and hitting each other before their vehicle went over the side.

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Alexandria's attorney, Kevin O'Brien, said the crash was a tragic accident.

Weiss said he had seen the sisters become violent towards each other before.

He was driving both sisters in a car when they asked him to pullover to buy wine. Weiss said he didn't want to.

"Anastasia turned around and she started kicking my right hand on the wheel, like she was trying to knock me over into the other lane," he said. Eventually, he managed to push her back into her seat, he said.

"Either one of them at any given second could go from just Jekyll to Hyde," he said.