In the three months since Milo Ventimiglia was reportedly seen cutting Hayden Panettiere's meat (no, that's not a euphemism) at a post-Emmys party, they've repeatedly denied reports of a hot and heavy off-screen romance.

But now, after frequent sightings of snuggly behavior, the "Heroes" co-stars (squickiness alert: they play uncle and niece) have apparently decided to take their first steps into coupledom with an assist from People, which has officially dubbed them "an item."

So serious is the relationship that Milo, 30, put in some time last month getting to know 18-year-old Hayden's New York City-based clan, reports the mag.

"He's even met her grandparents," enthuses a plugged-in "family friend." "He fits in perfectly with the family. Milo jokes around with her little brother. They're buddies."

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And while most parents would be less than thrilled if their button-cute teenage daughter were dating a guy a dozen years her senior, it seems Mama Panettiere is positively tickled.

"Hayden's mom adores Milo. She thinks he's so cute," the insider obligingly divulges. "She tells her friends that he's her boyfriend. She's very proud."

The duo known as Halo, whose camera-captured touchy-feeliness has ranged from handholding to slow-dancing, are "very affectionate and very comfortable around each other," the source adds to the mag. "They're not afraid to show their affection around her family and their friends."

Not surprisingly, given the infantilizing alleged steak-slicing incident, "He really takes care of her," says the mole, "even down to the little things like giving her a back massage and going with her to work things."

As for the fact that Ventimiglia was legally able to buy a beer right around the time Panettiere was mastering her multiplication tables and discovering the Judy Blume oeuvre, the chatty family snitch concedes it's an issue.

"At first it doesn't seem like there's a big age difference, but then you do see it," the source explains. "He's more proper and reserved, and she's still playful and very girly."

In Touch, however, says Milo was anything but reserved during dinner with the "Heroes" cast and producers on Dec. 15, when he supposedly paid tribute to Hayden in a toast.

"He called her his girlfriend and said that he loved her," claims a spy. "And they sat next to each other holding hands."

Panettiere's rep, who previously dismissed the dating speculation, tells People they "do not respond to inquiries from the media" about her "personal life."

As for Ventimiglia, he offered a non-denial denial when asked about the romance rumors in November, saying of the baby-faced blonde, "She and I are close friends. It's only natural that people are going to couple us together."

The frequently shirtless actor, whose dating history includes an extended liaison with his "Gilmore Girls" love interest Alexis Bledel, has seemingly had his smoldering eye on the starlet for a while.

When asked in December 2006 what he found "attractive" about Panettiere, who called it quits with age-appropriate reality show Z-lister Stephen Colletti at the end of the summer, he laughed, "Ask me Aug. 21 [Panettiere's 18th birthday], and I'll tell you a zillion things."

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