The 5'2" Bertinelli, who turns 47 this month, vows to lose 30 lbs. by September (from a size 14 to a size 8). Going public with her goal "is the motivation I need," Bertinelli says. "I need to do this in front of millions of people so I can't mess up."
And, she adds: "It is freeing because I can say it first: I know what you're thinking – I'm fat."
Bertinelli says that Alley, who has maintained her 75-lb. downsizing, also offered some advice: "She said, 'Even if Wolfie [the 16-year-old son of Bertinelli and her ex, Hall of Fame rocker Eddie Van Halen] wants to go to In-N-Out Burger, don't do it, because paparazzi will photograph you!' "
The Craig campaign, for which Bertinelli will shoot a new ad every month as she shrinks, represents a major step back into the public eye for the until-now stay-at-home mom whose last big TV role was on Touched by an Angel in 2003.
"Wolf is my priority," she says of her son. "I was a Hollywood hermit." Also, she admits, "I didn't like going up for interviews because I didn't want to hear how fat I am."
Although Bertinelli remains guarded about her current weight – "Tom [Vitale, her boyfriend of nearly three years] doesn't even know, and he's not going to until I get down" – she is blunt about her goals.
"I don't know how my size, 14, has become obese while size 0 is normal," she says. "It's insane. I'm not even going for a size 6. I'll be happy with a size 8."
For more on Bertinelli, including her 'rock-bottom moment' and how she let herself fall in love after her split from Eddie Van Halen, pick up this week's PEOPLE, on sale Friday.
