Kirstie Alley & Valerie Bertinelli's Feud REVEALED: Sitcom Rivalry Heated Up Before Weight-Loss Venture

Valerie Bertinelli is among the many stars who have shared their condolences for Kirstie Alley after her death at 71.

On Monday evening, the One Day at a Time actress posted a message in response to Alley's passing, tweeting "rest in peace" alongside a heartbroken emoji years after their rumored feud.

RadarOnline.com can report on how their friendship evolved years after insiders claimed they were in a behind-the-scenes battle in 2013 after Alley's sitcom came to TV Land while Bertinelli was starring on Hot in Cleveland.

It was perceived "as if there's not enough room for the both of them" at the network.

The tension was said to have grown after Alley, a former spokesperson for weight-loss giant Jenny Craig, brought Bertinelli on board as a celebrity endorser before parting ways with the company in 2007.

"She hoped sales would go in the toilet without her, but Jenny Craig's business boomed after Valerie signed on," said an insider.

Alley later revealed she put on 83 pounds, which Bertinelli was convinced she could easily shed.

"She should come work out with me!" the Touched by an Angel star told People. "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."

An insider said that while Bertinelli's remark was well-intentioned, the comments "just added fuel to the fire" at the time.

Bertinelli's 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 becoming best-sellers were also a reminder of her success.

Despite the rumored rivalry, Bertinelli and Alley have spoken very fondly of each other.

RadarOnline.com has since confirmed that Alley sadly died on December 5 after a brief battle with cancer, with her children stating their mom just found out she was ill.

Her sons, William True and Lillie Price, wrote in a statement: "We are sad to inform you that our incredible, fierce and loving mother has passed away after a battle with cancer, only recently discovered."

Looking ahead, this outlet has learned the Church of Scientology will hold a memorial for their longtime member at the Flag Land Base in Clearwater, Florida.