Dane -- who shot to fame amid six seasons on the hit ABC drama "Grey's Anatomy," where he played Dr. Mark Sloan, affectionately known as "McSteamy" -- said his symptoms began over one year ago, when he began to experience weakness in his right hand.

Eric Dane opened up about his recent ALS diagnosis on "Good Morning America," telling Diane Sawyer that he now only has "one functioning arm."

Eric Dane sits down with Diane Sawyer on 'Good Morning America' to discuss his ALS diagnosis and how his family — namely once-estranged wife Rebecca Gayheart, and daughters Billie and Georgia — has been his guiding force.