“THE BACHELOR” contestant Brooke Smith tearfully confessed on TV that her dad is in prison. But she said she was too embarrassed to explain why.

Now an ENQUIRER investigation has uncovered the shocking truth: Brooke’s 46-year-old father Billy Randolph Smith Jr. is a kiddie porn fiend and a serial rapist now serving a long prison sentence!

“He’s a wicked sexual deviant who preys on young girls,” said police Lieutenant Steve Isbell of Dyersburg, Tenn., Smith’s hometown.

Brooke, 22, of Albertville, Ala., is one of 25 contestants vying for bachelor Aaron Buerge on ABC’s hit television series “The Bachelor.”

On each episode, Buerge, 28, eliminates a few contestants and the last girl standing will win his heart.

Brooke is a front-runner, who shared a steamy hot-tub date with Buerge. In the October 16 episode, she told him her father is incarcerated, but she still didn’t tell him why.

And no wonder — according to court documents obtained by The ENQUIRER, Smith is a sex fiend with a criminal record that includes a long list of shocking offenses.

Smith was charged with one count of first-degree rape and two counts of first-degree sodomy 12 years ago.

His victim, Georgia Downs, claimed he broke into her home in the early hours of Dec. 31, 1989, and raped her at knifepoint. When Downs resisted, Smith slashed her and attempted, but failed, to force her into deviant sex acts.

Ultimately, the first-degree rape charge ended in a mistrial, and Smith was given probation for sodomy.

On May 25, 1992, Smith abducted a 14-year-old girl from a street in Boaz, Ala., drove her to his home and raped her at gunpoint. Smith was arrested and pleaded guilty to rape. He served just three years.

The rape victim’s mother told The ENQUIRER, “Billy Smith ruined my baby’s life. She has never been the same since Billy raped her. Billy robbed her of her childhood — and he’s robbed other innocent girls of theirs, too.”

In 1999, Smith struck again. “He met a 16-year-old Maryland girl over the Internet and actually went to her city twice and had sex with her,” Lt. Isbell told The ENQUIRER. “When she tried to end the relationship, Smith threatened to expose her by sending e-mails to her school. The girl told her mother, who alerted police.

“While we were investigating we found Smith had lured another 17-year-old girl to his house through the Internet. He had actually driven to her hometown in Ohio, picked her up and brought her back to Tennessee. Her parents thought she was dead!”

Smith was convicted of interstate transport of a minor for sex, using a computer to coerce, and possession of kiddie porn and is now serving time at Butner Federal Prison in North Carolina until 2011.

“I’m proud of my daddy,” Brooke insisted on the show.

One of Brooke’s pals told The ENQUIRER: “Brooke’s living in fear that other people will judge her because of her father’s mistakes. It’s eating her up inside. The reason she waited to tell Aaron Buerge about her father’s criminal history is because she was scared of getting booted off the show.”