"It was a lifestyle conflict," the mag quotes a source close to the couple. "They were in very different places. They are still on friendly terms. There are no hard feelings."
The insider says the split happened because their styles are rather different: "Panettiere is young. She likes to go out in the Hollywood scene and that's not his style."
Ventimiglia is apparently using the extra time to "concentrate on work on his production company, Divide Pictures."
The 19-year-old Hayden Panettiere and 31-year-old Milo Ventimiglia began dating in 2007, but didn't admit to being together until last year -- largely because of their 12-year age gap -- even though the relationship was hardly a secret by then.