They play niece and uncle on "Heroes," but are Hayden Panettiere and Milo Ventimiglia acting more like kissing cousins? The rumor mill has been churning in recent days with chatter that the age-mismatched but chemistry-laden co-stars may be getting cozy.

But in what's sure to be a crushing blow to many a fanfic forum, the easy-on-the-eyes pair adamantly deny there's anything untoward going on.

As expected, rumblings of an offscreen romance began shortly after the apple-cheeked starlet confirmed her recent bust-up with reality D-lister Stephen Colletti, whom she dated for about a year.

Later, TMZ.com spotted them strolling "arm-in-arm" outside another post-awards bash and boldly asked the burning hookup question, prompting Panettiere to shoot back, "I'm holding onto him because I'm about to fall over in these heels!"

"Hayden and Milo are cast mates and good friends," Panettiere's spokeswoman pooh-poohs to MSN Entertainment. "There is nothing further to their relationship and all reports to the contrary are false."

A mouthpiece for Ventimiglia, who was briefly linked to Emmy Rossum after calling it quits with onetime "Gilmore Girls" amour Alexis Bledel, is also quick to downplay the dating reports, telling us they're just "not true."