A New York man was stunned to find out that his four-year-old twins were not an accidental pregnancy after all -- but that his desperate girlfriend secretly stashed away his sperm and used it for an in-vitro procedure, he charges in a lawsuit.

Joseph Pressil, 36, was not planning on having children with Anetria Burnett, with whom he was in a relationship for six months in 2007, he said.

So she took matters into her own hands, he told the New York Post, in order to remain in his Texas house and make a legal bid for half of his possessions.

"A gold digger is an understatement. She was trying to get community property and alimony. She's ruthless," he said.

Now, Pressil is suing Burnett in Texas for custody of their sons.

"This is more than a nightmare -- it's a horror story," he told the Post.

Pressil, a telecommunications manager, said he hooked up with Burnett, 34, when he lived in Texas -- and was a little surprised when she announced she was pregnant.

"We always used condoms," he said. But when a DNA test proved him to be the father, Pressil said he began paying $800 a month in child support.

"At first, I doubted [the children were mine], but I figured I would wait until the twins were born," he said. "But when the kids were born, they looked just like me."

The real bombshell dropped last February, when Pressil got a strange receipt in the mail for sperm cryopreservation.

Confused, he called the company that had sent him the paperwork, which referred him to the Advanced Fertility Center of Texas, where a manager asked him to sign a release form.

That is when he said he uncovered the bizarre plot.

"She was taking [the semen in condoms] after the fact and running down to the clinic with it," said Jason Gibson, who is representing Pressil in his suit. He now has joint custody.

The fertility clinic's manager simply assumed he and his ex were married when she got the successful in-vitro fertilization procedure that resulted in the birth of the twins, his suit says.

Pressil then said he confronted Burnett, an exotic dancer, who allegedly told him, "Oh you're not stupid. I thought you knew."

"Her reason for doing it was to stay in the home -- because I had told her she had to leave my house when we broke up," he said.

She even filed to have him declared her common-law husband, he said, which would have entitled her to half his property. The filing was denied.

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