Ian Somerhalder and Nina Dobrev's split was ''inevitable''.

The 'Vampire Diaries' co-stars have ended their three-year romance and while there is no one else involved in the break-up, friends believe the 10 year age gap between them was a factor.

A source close to Nina, 24 and Ian, 34, told Us Weekly: ''There was no mean spiritedness behind of either of their motives for ending it.

''The relationship kind of brewed out of a friendship and the fact that they had to get into a romance for the show. The breakup was inevitable.

''I think she decided she wanted to experience other things.''

The couple met on the set of the hit US TV show - in which Nina plays Elena Gilbert, a high school student torn between vampire brothers, Damon (Ian) and Stefan (played by Paul Wesley) Salvatore - in 2009 but they didn't go public with their relationship until 2011.

The former flames will avoid any awkward encounters in the immediate future as the fourth season of 'Vampire Diaries' has already wrapped production, but they are expected to return to the show's Atlanta, Georgia set in July for filming of the fifth season.