The Die Hard star suffered with the language disorder as a child and when he was being assessed doctors didn't think it was a sign he was suffering from the neurocognitive disorder, but was later diagnosed with frontotemporal dementia in 2023.
Speaking to Town and Country magazine, his wife, Emma Heming Willis, 46, said: "He had a severe stutter as a child. He went to college, and there was a theatre teacher who said, 'I've got something that's going to help you.' Bruce has always had a stutter, but he has been good at covering it up. So, when he began to experience difficulties with language, it seemed like it was just a part of his stutter.
Tallulah Willis (centre) says she knew something was wrong with dad Bruce Willis "for a long time". (AP PHOTO)
"Never in a million years would I think it would be a form of dementia for someone so young."
The 69-year-old Hollywood star had initially been diagnosed with aphasia, a language disorder that affects a person's ability to speak and understand others, in 2022.
Willis and his ex-wife Demi Moore's daughter Tallulah, 30, previously admitted she knew something wasn't right with her dad before his diagnosis.
In an essay for Vogue, Tallulah penned: "I've known that something was wrong for a long time. It started out with a kind of vague unresponsiveness, which the family chalked up to Hollywood hearing loss: 'Speak up!' Die Hard messed with Dad's ears.
"Later that unresponsiveness broadened, and I sometimes took it personally."
Willis also has Rumer, 36, Scout, 33, with Ghost star Moore, and two daughters, Mabel, 12, and Evelyn, nine, with his current wife, Heming Willis.
Tallulah added she felt like her dad had "lost interest" in her when he had his daughters with Heming Willis and was struggling with an eating disorder as his condition worsened.
She said about her fear he was focusing too much on his new family: "Though this couldn't have been further from the truth, my adolescent brain tortured itself with some faulty maths: I'm not beautiful enough for my mother, I'm not interesting enough for my father…I admit that I have met Bruce's decline in recent years with a share of avoidance and denial that I'm not proud of.
"The truth is that I was too sick myself to handle it. For the last four years, I have suffered from anorexia nervosa, which I've been reluctant to talk about because, after getting sober at age 20, restricting food has felt like the last vice that I got to hold on to… by the spring of 2022, I weighed about 84 pounds (38 kg).
"I was always freezing. I was calling mobile IV teams to come to my house, and I couldn't walk in my Los Angeles neighbourhood because I was afraid of not having a place to sit down and catch my breath."
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