AceShowbiz - Sophia Bush has revealed she and her "One Tree Hill" co-star Austin Nichols have been dating for the last four years. The actress was rumored to have started a relationship with Nichols last year after they were spotted being intimate at the Hollywood Style Awards in October 2009.

But now Bush has opened up about the romance, admitting she and her beau actually started dating in 2006 - two years before Nichols even started working on the U.S. TV drama. And the star is smitten with the actor, who took a job on "One Tree Hill" in 2008 and moved to be closer to her.

She says, "We've been dating off and on for the past four years. I was pretty terrified. We had so many years of history prior to him coming to work on the show, and I think someone taking a job and moving their life across the country to show you how much they care is pretty much the most romantic gesture that a person could make."

Bush was briefly married to former "One Tree Hill" star Chad Michael Murray in 2005.