Kat Dennings on Losing Her 'Soulmate Cat' and Adopting Two 'Fantastic' Kittens: 'They Save You' (Exclusive)

The actress is the face of Fresh Step’s limited-edition 'Garfield Movie' box, which supports Best Friends Animal Society

Kat Dennings doesn't just identify as a cat lady — she wears the title like a crown.

From her first feline love, Daisy, to Pumpkin, a stray who wandered into the actress's life and made her think she'd "never love again," Dennings has "always been a cat person," she tells PEOPLE from Best Friends Animal Society's Los Angeles Pet Adoption Center.

More recently, the WandaVision star's life was changed by the unexpected death of her "soulmate cat" of over a decade, Millie, last fall.

"It was very unexpected and horribly traumatic, and I was like, 'What do I do? I still can't believe this.' I thought she was going to live to be 30, and it was just the worst," the star, 37, recalls. "But a friend of mine was like, 'Just get another cat right now. Just don't wait eight years like you did last time.'"

So Dennings did just that — and found that good things often come in pairs.

"I found these two little sisters, Lentil and Barley, who are wonderful and so funny and completely different from Millie, and it's healing," Dennings says. "I mean, it doesn't take away the pain, but it's amazing."

Related: Kat Dennings Shows the Wedding Floral Arch She Built Herself: ‘Three Days of Literal Blood, Sweat and Tears’

Though not fated to be "an insane lover of cats" like Dennings, her husband, Andrew W.K., also enjoys life with the kittens — who quickly became "daddy's girls," she says.

"He loves animals. But with cats, because he's allergic, he never really engaged," the actress tells PEOPLE. "I know he was scared, but now he loves them."

The 2 Broke Girls star is glad the kittens have her, her musician husband, and each other because the hardest part of being a pet owner "is probably just having to leave them for the day," she says. "That's really tough."

Related: Kat Dennings and Andrew W.K.'s Relationship Timeline

Dennings hates to see a lonely feline, which is why she adopted Lentil and Barley as a twosome — and why she is excited about teaming up with Fresh Step and The Garfield Movie to support Best Friends Animal Society in their mission to make all U.S. animal shelters no-kill.

Fresh Step is selling limited-edition Garfield boxes through June 9. The purchase of each box triggers a litter donation — up to one million pounds of litter — to Best Friends' life-saving centers across the country, which the Dollface star has supported for years.

"Cat adoption is one of my passions. It's so important to me," Dennings says, adding, "It's always great to get them in pairs — or threes or fours, I'm very tempted — but then they can keep each other company when you're out."

With Millie, Dennings "always rushed home" from work. "But now that I have two, it's really like they keep each other company, which is fantastic," she says. "They could care less if I'm out of the room. They're like, 'Whatever, lady.'"

The Marvel star has embraced the kittens' "whatever" attitude as a lifelong Garfield lover and an actress who, in her experiences working with felines on set, cannot help but worry for the animals' well-being.

"This is why Garfield's good for me, because it's not a real cat, so I can enjoy it," she says. "If I see a real cat in TV or movies, I get very stressed out for the cat ... I'm like, 'Is it okay? Does it want to be an actor? Does it want to be here?'"

And it doesn't help that "every time I see a cat or work with a cat, I fall in love," Dennings adds. "It's difficult."

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Dennings and her husband have a full (and furry!) house, and they encourage everyone to embrace cat lady-dom — especially by adopting rescue felines.

"If you just search, there’s always whatever breed you can think of,” the actress says. “You might just have to wait, but there's always an adoption thing because there are these precious little angels sitting and waiting for their loving homes and just needing families.”

"People would ask if Millie was some special breed and I was like, ‘I think she's part squirrel. I don't know,'" she jokes, adding, "You really can find the most special, incredible loves of your life by adopting."

“There's nothing like it, ‘cause you’re saving them, and then they save you.”

The limited-edition Garfield box of Fresh Step litter is available exclusively at Walmart, and The Garfield Movie is in theaters on May 24.

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