Just months after revealing his ALS diagnosis publicly, actor Eric Dane speaks out for the first time in a interview with Diane Sawyer about the moment he first noticed the warning signs, and more.

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.