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The woman who was dating a Colorado dentist when he allegedly poisoned his wife with cyanide-laced protein shakes to be with her said he had lied about his marriage.

In her first interview, Karin Cain, an Austin-based orthodontist, told ABC News that James Toliver Craig, 45, had duped her.

"If I had known what was true, I would not have been with this person," Cain said."I didn't willingly have a relationship with someone who was in a marriage."

The clip aired Wednesday morning the same day that Craig was due in Arapahoe County District Court for prosecutors to try to persuade a judge that there was enough evidence to try him for first-degree murder. 

COLORADO DENTIST ACCUSED OF POISONING WIFE'S PROTEIN SHAKES TO START NEW LIFE WITH LOVER

Angela and James Craig smiling in a family portrait.

Colorado dentist James Craig, right, is accused of fatally poisoning his wife and the mother of his six kids, Angela Craig. (Facebook)

He is accused of killing Angela Craig, his wife and the mother of his six children, with cyanide and arsenic, which caused her to suffer a seizure on March 15 that left her brain-dead. She was later removed from life support.

Cain said she met Craig at a dental conference in late February. The mother of two was in the midst of a divorce, and Craig told her he was too. 

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"He told me they hadn’t been living together. He had an apartment," she said.

Days later, he started poisoning his wife of 23 years, according to an arrest affidavit.

James Toliver Craig mugshot

Denver dentist James Toliver Craig is accused of fatally poisoning his wife with cyanide and arsenic. (Aurora Police Department)

"There was a lot of just feeling like so connected," said Cain, who added that they had never consummated their romantic relationship. 

One day after Angela Craig's seizure from a mysterious illness that initially baffled doctors, Cain reluctantly flew into Denver for a preplanned trip. 

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She suggested canceling the jaunt, but her new boyfriend told her he could use the support.

They had dinner twice, but Angela Craig's dire condition did not appear to trouble the dentist.

Texas orthodontist Karen Cain show with her two children shown with her two children an unidentified male.

Texas orthodontist Karen Cain, the former mistress of dentist James Toliver Craig, who's accused of fatally poisoning his wife, shown with her two children. Cain was in the midst of a divorce when she met Craig. (Facebook)

"He at no point seemed stressed or anxious," she told ABC News. After she read the detailed arrest affidavit, Cain said she was stunned. 

"There is no way I’m motive. There has been no planning a future together," she recalled of her thoughts. However, the timeline in the affidavit suggested otherwise.

Cain, whose romance with Craig lasted a total of three weeks, now finds herself in the middle of a murder investigation

James Craig in face mask with giant hole in it, smiling Craig in button shirt at right

Two photos of dentist James Oliver, who is accused of murdering his wife, Angela Craig. (Facebook)

Angela Craig had repeatedly gone to the hospital in the prior weeks for unexplained symptoms, including severe headaches and dizziness. 

Police launched an investigation after James Craig's business partner and friend, Ryan Redfearn, contacted authorities after a can of potassium cyanide was delivered to their dental practice.

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Investigators soon accessed Craig's browsing history on his work computer, which revealed searches for "How many grams of pure arsenic will kill a human?" and "Is Arsenic Detectable in Autopsy?"

James Craig center in family portrait, wife to his right

Angela and James Craig in a family portrait. James has been charged with first-degree murder for allegedly poisoning his wife. (Faceboook)

They also found several orders he had allegedly placed for various poisons.

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An attorney for Craig did not immediately return a request for comment.

Craig is being held in jail in lieu of a $10 million bond.