Comedian Andrew Dice Clay has been diagnosed with Bell's palsy.
The A Star Is Born actor, 63, noticed his face was drooping several weeks ago, his representative told TMZ.
He then went to a doctor to check whether he'd had a stroke, despite having no other symptoms, and was diagnosed with the condition - which causes facial muscle weakness or paralysis.
As Bell's palsy is not usually permanent, he has been told symptoms should subside in a few weeks, and has already worked his illness into his controversial stand-up act.
Dice Clay addressed the issue at a gig in New Jersey earlier this week, which was attended by his A Star Is Born co-star Lady Gaga.
The veteran funnyman posted images of himself performing despite displaying visible symptoms of Bell's - as his mouth was drooped to one side - on Instagram.
"It Don't Matter ... Palsy Face Or Not !!!," he captioned the photos of himself onstage.
Dice Clay, who played the father of Gaga's singer character in A Star Is Born, also paid tribute by posting snaps of himself with her backstage - revealing that she'd also given an impromptu performance.
"And Of Course It Was Great To See My On Screen Daughter @ladygaga," he wrote. "It Was A Fun Hang. She Did A Stellar Performance From Her Burlesque Old School Moves To Her Absolutely Powerful Vocals. Cause It Don't Mean A Thing If It Ain't Got That Swing!!!"