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.

The San Francisco-born star of ‘Grey’s Anatomy’ and ‘Euphoria’ has been on Good Morning America this week to discuss the frightening realities of amyotrophic lateral

Now, however, the actor has shared a few more sobering updates about his health on Good Morning America. “My right side has completely stopped working,” he told the program. Dane said that he expects to lose control of the left side as well.

ALS, short for amyotrophic lateral sclerosis, is a degenerative neurological disorder that eventually leads to paralysis, taking away a person's ability to move, speak, swallow or even breathe, according to the National Institutes of Health.