Eric Dane is facing the brutal truth of his ALS diagnosis — and it’s hitting hard, ’cause he got choked up revealing how he’s now down to just one functioning arm … and even that might not last much longer.

The “Euphoria” star dished all on “Good Morning America” … explaining while his left arm is still working, he can feel it getting weak, and knows that one will probably be out of commission in a few months too.

It’s not just his arms — the 52-year-old says his legs are next … recalling a terrifying snorkeling trip with his daughter where he ran out of strength, and she had to pull him to safety.

Eric says he’s angry about the diagnosis — especially after losing his own dad to suicide at age 7, he now fears his his two daughters might lose him way too soon.

It’s been a lot for Eric to process since revealing his ALS diagnosis back in April — especially after the exhausting road just to get accurate answers. He bounced from one specialist to another, test after test … until a neurologist finally dropped the bomb: ALS (amyotrophic lateral sclerosis) — three letters he says haunt him from the moment he wakes up every day.

Despite it all, Eric held it together — until he brought up his wife, Rebecca Gayheart, being his rock, his biggest support … and that’s when the waterworks hit.