During a sit-down interview with Diane Sawyer on "Good Morning America," Eric Dane opened up about his harrowing ALS diagnosis and navigating the heartbreaking effects.

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.