An Instagram post said Willis had aphasia, a language disorder that robs people of their ability to communicate.

"Bruce has been experiencing some health issues and has recently been diagnosed with aphasia, which is impacting his cognitive abilities," the post reads. 

"As a result of this and with much consideration, Bruce is stepping away from the career that has meant so much to him."

Aphasia is typically caused by a stroke or head injury, though it can come on gradually and progressively in rare cases. The condition affects a person's ability not only to speak and understand verbal communication, but also to read and write.

Los Angeles Times reported that questions about Willis's short-term memory have been circulating recently.

The paper noted that he was not at the Oscars on Sunday, when several other stars of Pulp Fiction, including Samuel L. Jackson, Uma Thurman and John Travolta, took to the stage.

Willis has been a fixture on the small and large screens since the 1980s, coming to public prominence in the TV series Moonlighting.

But it was as hard-bitten hero John McClane in Die Hard that he became a bankable major star of the cinema, sparking a career that has generated billions of dollars in box office receipts.

Willis, who turned 67 this month, also provided the voice for the baby in the popular family flick, Look Who's Talking. 

Another of his best-known roles is as a psychiatrist in The Sixth Sense opposite Cole Sear, a boy who sees “dead people” played by actor Haley Joel Osment.

Willis won a Golden Globe and two Emmys during his career, but was the recipient of a far less welcome honor last weekend, Worst Performance by Bruce Willis in a 2021 Movie, a special category at the Razzies.

The Instagram post announcing the news of his retirement is signed by Willis' current wife, Emma Heming Willis, as well as his former wife, actress Demi Moore, and his children Rumer, Scout, Tallulah, Mabel and Evelyn.

"This is a really challenging time for our family and we are so appreciative of your continued love, compassion and support," it adds. 

"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.

"As Bruce always says, 'Live it up' and together we plan to do just that."

Reaction was swift from fellow stars.

Jamie Lee Curtis wrote, "Grace and guts! Love to you all," while Cindy Crawford posted an emoji of praying hands.

Actress and former costar Elizabeth Perkins wrote, "Sending so much love to you all."