As Radar has reported, Tad was recently arrested when he and Thomas were finally found in a remote Northern California area together after vanishing for five weeks.
While the girl was reunited with her family, Tad faces one federal count of transporting a minor with the intent to engage in sexual activity across state lines.
And in a shocking Inside Edition exclusive, Jill told the TV show that she and her husband, 50, had both been trying to help Thomas get through some tough times at home.
As Radar learned, Thomas' dad had claimed in divorce papers that the teen was abused by her mom Kimberly Thomas before the disappearance.
Incredibly, at first, Jill didn't have a clue that a romance was brewing between Tad and his under-aged pupil—and she even thought of her as a surrogate daughter!
"I feel slightly betrayed by her because she knew me," Jill said to the newsmagazine. "I don't really want to talk to her. It's not the right time. Maybe one day."
Jill did say eventually, she warned her husband against getting too close to youngster Thomas after noticing some overly friendly moments between the two.
In March, they disappeared together from Tennessee, where Tad had worked as Thomas' teacher.
"He was getting really close to her," Jill explained, but insisted it appeared to be "a father-daughter close, a friendship close, and I knew that. I discussed that with him. And explained to him, 'She's your student, you can't be so close to her.'"
Jill added to Inside Edition, "Never did I think there was a romantic thing between the two of them. There were no signs of that."
However, as Radar has reported, others saw signs and the two wrote each other love letters before vanishing together.
Jill, who has filed for divorce from Tad, said that her husband exploited the girl.
A Thomas family rep has stressed that Cummins is a "classic predator" who groomed her to run off with him.
Meanwhile, Cummins' daughter Ashley, 26, is standing by her dad—as well as her mom.
"He was the definition of what a good father should be and he still is," Ashley told Inside Edition. "I believe that. He needs to at least know that everybody's not against him."
Ashley has vowed to visit her father in jail.
Cummins faces a minimum sentence of 10 years and up to life in prison, if convicted.
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