AS KIRSTIE ALLEY brings her new sitcom to TV Land, she’s ignited a bitter behind-the-scenes battle with her former friend VALERIE BERTINELLI, a source says.

Kirstie’s self-titled show launched on Dec. 4, joining Valer­ie’s “Hot in Cleveland,” which has been a huge success on the cable network.

“They used to be friends, but NOW Kirstie hates Valerie’s guts,” said a Hollywood insider. “Kirstie is joining TV Land and she’s trying to undermine Val as if there’s not enough room for the both of them.”

Kirstie recently took a jab at Valerie on Twitter, suggesting that the for­mer “One Day at a Time” actress had hooked up with Kirstie’s ex-husband, Parker Stevenson. The li­aison supposedly occurred when Valerie – who was just 18 at the time – guest starred in a 1978 episode of “The Hardy Boys/Nancy Drew Mysteries.”

“Ummm, were you messin’ with my man back then?” Kirstie tweet­ed, along with a photo from the set.

Valerie tweeted in response: “Ha! I was jailbait back then.”

While Valerie good-naturedly tried to pass the whole thing off as a joke, the insider says Kirstie was dead serious.

“Even though she wasn’t mar­ried to Parker back then, Kirstie remains insanely jealous of any woman she thinks he’s had a tryst with – especially Valerie,” said the insider. “The truth is, Valerie makes Kirstie sick because she beats Kirstie at virtually everything she does.”

As The ENQUIRER reported in 2010, Kirstie has a long-harbored hatred toward Valerie for success­fully losing weight – and keeping it off.

It was Kirstie, a former spokes­person for weight-loss giant Jenny Craig, who brought Valerie on­board as a celebrity endorser for the company in March 2007.

The next year, Jenny Craig dumped Kirstie for piling the pounds back on.

“Kirstie was outraged and hu­miliated over her ouster from Jenny Craig,” said the insider. “She hoped sales would go in the toilet without her, but Jenny Craig’s business boomed after Valerie signed on.”

Valerie tried to extend an olive branch to Kirstie, suggesting that she could help her lose the more than 83 pounds she’d gained back.

Valerie said at the time: “She should come work out with me!

“She should remember you can’t do everything in one day (and) her exercise has to be consistent. She can do this. There’s no doubt in my mind.”

The insider said Valer­ie’s comments were like “adding insult to injury” for Kirstie.

“She felt that Val was rubbing her nose in her failure,” the insid­er continued. “It just added fuel to the fire.”

Valerie also has had two top-selling books – “One Dish at a Time: Delicious Recipes and Stories from My Italian-Ameri­can Childhood and Beyond” and “Losing It: And Gaining My Life Back One Pound at a Time.”

But former “Fat Actress” Kirstie was looking better than ever two years ago after her appearance on “Dancing with the Stars.” Thanks to her grueling practice sessions – and the work she put in after the show ended – she managed to drop 100 pounds. Since then, however, she’s ballooned back up again.

Valerie, on the other hand, still looks great and has kept off the 47 pounds she lost with Jenny Craig.

Valerie has even beat Kirstie in love. The 53-year-old wed former financial planner Tom Vitale in 2011 while Kirstie, 62, continues to come up empty in the romance department.

“Seeing Valerie is a reminder to Kirstie of all her failures, so she’s largely avoided her,” said the insider. “But that’s going to be difficult now that they both  have shows on TV Land.”