Bruce Willis is said to have recently been diagnosed with the condition aphasia, with his family having revealed that as a result he will be stepping away from his career.
This was announced on social media yesterday, with them stating that it had been a "really challenging time" amid his health issues which have impacted his cognitive abilities.
The actor, 67 - who is best known for playing John McClane in the Die Hard franchise - will have brought recognition to the condition, which fans might not have heard of before.
Aphasia is understood to typically be caused by damage to the left side of the brain - such as following a stroke - and often presents itself as difficulty with language or speech.
According to the NHS, people experiencing the condition can have difficulty with reading, listening, speaking and writing - though it's generally associated with speech issues.
It states: "Speaking problems are perhaps the most obvious, and people with aphasia may make mistakes with the words they use." However, it "doesn't affect their intelligence."
The condition is said to be caused by damage to parts of the brain responsible for understanding and producing language. There are several possible causes of such.
The NHS notes that the most common cause of aphasia is a stroke, though it can also be brought on by severe head injury, a brain tumour and neurological conditions.
It can affect people of all ages though typically is seen in those over the age of 65, with the main form of treatment for the condition being speech and language therapy.
The success of such therapy can depend on the cause of aphasia, with most of those who have it following a stroke able to recover to some degree with treatment.
Bruce's family have not yet disclosed the circumstances surrounding his aphasia diagnosis, having only said that he had been experiencing "some health issues" prior.
The Mirror approached his reps for comment.
His departure from acting was announced in a statement issued by his family on social media yesterday, which was signed by his close relatives, including his five daughters.
It read: "As a family we wanted to share that our beloved Bruce has been experiencing some health issues and has recently been diagnosed with aphasia, which is impacting his cognitive abilities."
The family said as a result and "with much consideration" he is "stepping away from the career that has meant so much to him" - which has seen him win several awards.
They continued in the statement: "This is a really challenging time for our family and we are so appreciative of your continued love, compassion and support."
"We are moving through this as a strong family unit, and wanted to bring his fans in because we know how much he means to you, as you do to him," the family continued.
They said that Bruce - whose film credits include Pulp Fiction, The Fifth Element and the Sixth Sense - always says "live it up," with them planning to do just that together.
It was signed by his wife Emma Heming Willis, 43, ex-wife Demi Moore, 59, and his daughters; Rumer, 33, Scout, 30, Tallulah, 28, Mabel, nine, and Evelyn, seven.
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