Milo Ventimiglia and Hayden Panettiere officially a couple!

Bloggers say that Ventimiglia announced that he and 18-year-old Panettiere were dating when he toasted the actress at a pre-Christmas Water Grill party in Los Angeles. Milo evidently told his co-stars that he was dating Panetierre and even told said he loved her.

"He called her his girlfriend and said that he loved her," an eyewitness says.

Sources say that Milo and Hayden spent the rest of the evening holding hands.

This is not the first time the actor is linked to his co-star. He and fellow former "Gilmore Girls" star Alexis Bledel dated for more than three years.