REVEALED! The baby making drama hunky SEAN LOWE is hiding from finalists. PLUS: host CHRIS HARRISON hits on his married sister!

 THE BACHELOR” hunk Sean Lowe was ready to give his beloved, childless sister the ultimate gift of a baby, The ENQUIRER has learned exclusively.

In a startling story of true devotion – and hidden from the beautiful ladies on the show – Sean had offered to donate his sperm to a surro­gate so his older sister Shay could have the child she so badly craved.

Shay and her husband Andrew Shull had experienced heartbreaking infertili­ty problems, leading to six unsuccessful intrauterine inseminations over a 13-month period at a cost of more than $20,000.

“Not only were Shay and her husband devastated, so was Sean,” revealed a family insider. “Family is everything to him and having kids is a big part of it. But month after month, he heard the same disappointing news, his sister wasn’t pregnant.”

To bring the joy of a child into their lives, Shay and Andrew began talking about adopting.

That’s when Sean, who’d introduced Shay and his college football teammate Andrew, came up with the idea of donating his sperm to a surrogate, so his sister could have a baby with at least some of her family’s genes.

But just when Sean was set to make the offer to his sister, she announced fantastic news – she was finally pregnant. Incredibly, she eventually had two babies, a boy and a girl.

“I struggled with infertility, did a lot of fertility drugs and then bam! I had two babies without drugs and without trying… thank you, Jesus (times two!)” Shay wrote on her blog.

Despite her family bliss, blonde stunner Shay raised eyebrows when she gushed over recently separated “Bachelor” host Chris Harrison on her blog after the two spent time together during filming of the show in St. Croix.

It was Shay’s 31st birthday and she was there without her hubby and kids. Harrison, 41, apparently swooped in to make her birthday very special.

SHAY SHARED PHOTOS OF HER “TRIP of a lifetime” on her blog, writing “Birthday love with Chris! He sat and talked to me for about an hour…I heart Chris.” Now, sources say Sean better keep an eye on his sister because dad-of-two Harrison has been desperately looking for love since splitting from his wife of 18 years, Gwen Jones, 41, last May.

“Now that Chris is single, he’s on the prowl for a new ladylove,” said a source. “He was really put­ting the moves on Shay, and she seemed to love the attention.

“The entire cast and production crew picked up on it. He didn’t even try to hide it.”