The two Heroes co-stars, Hayden Panettiere and Milo Ventimiglia, have announced their split, reports UsMagazine.com.
A source close to the couple stated, "It was a lifestyle conflict. They were in very different places."
The source added, "They are still on friendly terms. There are no hard feelings."
The two stars, who began dating in 2008, kept their relationship secret for several months, mostly because of their 12-year age difference.