Ali Larter and her fiancé celebrated their engagement in style Saturday night with a party at L.A.’s Sunset Tower Hotel.

The Heroes star and actor Hayes MacArthur were joined by about 100 friends, who sipped drinks from a private bar and sat on comfortable leather couches inside the hotel or mingled by the pool and terrace area with its stunning views of the city.

In a toast to his “wife-to-be,” MacArthur recalled how the couple wore loin cloths on the set of the 2007 comedy Homo Erectus in Austin, Texas.

“In that moment I knew how much you meant to me, how much you care about everything you do and everyone in your life,” he told Larter, 32.

The couple have dated for five years and became engaged in December, but taking it slow may not have been Larter’s idea.

“I told my boyfriend after three weeks that I wanted to marry him and that we could do it tomorrow,” Larter, told Cosmopolitan last year. “I look forward to that time when I’m home with babies.”

It will be the first marriage for both.

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Heroes star Ali Larter and her longtime boyfriend, actor Hayes MacArthur, got engaged over the weekend, PEOPLE confirms.

“It’s true,” says a rep for the actress. “They’re thrilled.”

This will be the first marriage for both. No wedding date has been set.

“I told my boyfriend after three weeks that I wanted to marry him and that we could do it tomorrow,” Larter recently said. “I look forward to that time when I’m home with babies.”

And in August, Larter she was madly in love, adding that MacArthur has “brought light to my life. I feel lucky every morning when I wake up and see him.”

Keeping heroically fit doesn’t come easily to Ali Larter - despite some noticeable physical advantages.

“When I’m in really good shape, I like my butt. It’s juicy - that’s what my fiancé says,” the Heroes actress, 32, referring to actor Hayes MacArthur, tells Allure for its July issue.

“I’m an indulger, but then I have to be good,” Larter says over a large lunch of dumplings, scallops with ravioli and a burger with salad, fries, ketchup and mayo. “I’m also going to get my butt out and go for a run tomorrow.”

“The faxes went out from the producers and the director to my agents to my manager to call me and ask me to lose weight,” she says. “I just remember sitting in my trailer hysterically crying from the embarrassment I felt about myself, my body - and that no one could talk to me directly.”

But she realizes that it was nothing personal - only business. “This is what I signed up for,” she admits. “What I do for a living puts me in the spotlight. They pay me for it.”

Heroes star Ali Larter won’t reveal the identity of her boyfriend, but it sounds like he may be her knight in shining armor.

“I’m madly in love,” the 31-year-old actress and model tells InStyle Makeover’s fall issue. “He just brought light to my life. I feel lucky every morning when I wake up and see him.”

Hopefully the mystery man likes children, because Larter sees them in her future - after her career calms down a bit.

“I’m loving this right now,” she says of acting. “But I can’t wait for that.”

Larter, who plays Niki Sanders on NBC’s Heroes, spent many years modeling before she caught the acting bug. But growing up, she was hardly the most beautiful girl on the block - more tomboy than TV star.

“I had a bowl haircut,” she says. “My face was always flushed, and I had one big tooth. I was the sweaty dirty girl, and I’d come home with one sock up, one sock down.”

Now that she’s found success, Larter says, she and her boyfriend are doing a good job staying balanced, knowing when to turn things up and when to chill out.

“Last night I was in my skintight Brian Reyes dress and Louis Vuitton heels. …Today I packed my weekend bag - cargos, sneakers and sweats,” she says. “And you know what? I need both. Balance is something that we all strive for, but for me it’s to make sure my life has enough downtime, plus a bit of play.”

Ali Larter may play a heroine on television - but she’s also just as bold in real life.

The New Jersey native, 31, has no qualms about speaking her mind when it comes to men, diet or how she stays fit in Hollywood.

“I told my boyfriend after three weeks that I wanted to marry him and that we could do it tomorrow,” Larter tells Cosmopolitan in its October issue.

And while such a pronouncement might scare off some men, the Heroes star and her boyfriend - actor Hayes MacArthur (who appears in the upcoming film The Game Plan) - have been steadily dating for two years.

“Now that I’m actually in love, I know that what came before wasn’t real,” she says. “It’s about being there for each other through the ups and downs of life.”

In terms of the future, she says, “I do want to get engaged and married … and I look forward to that time when I’m home with babies.”

Another issue where Larter is equally brazen: Her approach to diet, especially given Hollywood’s rigid standards for female stars. “I love wine, bread and cheese,” she says in the interview. “I just have to cut out the bread sometimes.”

Larter, who characterizes her approach to food as being “just like every other girl,” explains that it’s all about moderation and balance. “Last night, I drank some merlot and made potatoes au gratin with a rib-eye steak,” she says. “It was amazing. I hope to always find that balance.”

Her sense of moderation also translates into her exercise regimen. Put

simply, Larter tells the magazine, “I don’t want exercising to take over my life completely.” So to stay fit, she takes runs and hikes with her dogs.

For Larter, her approach to life - and her attitude - stem from growing up on the East Coast and nurturing a career largely outside of the Hollywood system.

“I’ll always be a Jersey girl,” she says. “I don’t always get my way, but

you’ll know exactly how I feel about it.”