She began sleeping with him when he was her 12-year-old student, had two kids by him, and spent more than seven years behind bars for child rape in a twisted tale of obsession that stunned the world.

Now shamed teacher Mary Kay Letourneau (search), freed from prison last month, is about to shock again — by marrying her former child lover Vili Fualaau (search).

"We've always planned that and it hasn't changed," Letourneau tells Barbara Walters (search) tonight on "20/20."

And, she says, they may have a third child together, boasting that "I'm healthy enough."

Letourneau, 42, served 71/2 years on a 1997 child rape conviction for her affair with Fualaau at a Seattle area school.

Pregnant during her first arrest, the temptress teacher served six months and was ordered to stay away from her jail-bait lover.

But after she was sprung, she was caught having sex with Fualaau in her car and sent back to prison — where she gave birth to Fualaau's second baby.

And while she was forbidden to see or speak to him during her long stretch, she and Fualaau, now 21, quickly hooked up the moment she was released in August.

Letourneau tells Walters her lust for the youngster began innocently enough in the fall of 1991, when he was in her sixth-grade class.

"Well, there was an emotional attraction . . . we just had bonded . . . I also knew he had girl interests.

"And I did suspect, oh, I knew definitely, it was extending in my direction," she says.

"One time he just came straight out and said, 'Would you ever have an affair?' . . . He wasn't even 13 yet . . . I thought to myself, 'Do not look him in the eyes.'

"He knew that I was avoiding all of his comments and insinuations and he was very assertive and wanted a response . . . He said he was in love with me."

Married with four kids, Letourneau says she soon realized "I felt a very deep love for him.

"He said, 'How old do you think you're going to be when you die?' and I said, 'Oh, well, I'll probably be 100 like my grandmother,' and he said, 'Well, then I'm going to be 80 when I die, because I'm not living another day on this earth without you.'

"And that might sound simple to say, but he didn't say it in a simple way to me, and I started to realize that he is very serious about his feelings, and this is not a crush he is dealing with," she tells Walters.

"There was a kiss, and I thought, 'That's OK, but it's not going to go any further.' "

But it did.

"The incident was a late night that it didn't stop with a kiss, and I thought that it would, and it didn't," she said.

After her arrest, Letourneau said she defied a court order that she not see Fualaau because "he was the father of my newborn, we loved each other and the worst that could happen was that I would go to prison."

She didn't see him for over seven years.

And now, she says, "I just, I can't imagine traveling and seeing something without him, learning together, being with him, supporting him for what he would like to do in this life."