The brain disorder can cause a variety of life-altering symptoms, such as memory loss and inability to perform regular functions.
Now, the Red actor’s 29-year-old daughter has let on just how easy it is to miss the early symptoms of the illness, admitting that she and her family knew “something was wrong” with her father “for a long time”.
“It started out with a kind of vague unresponsiveness, which the family chalked up to Hollywood hearing loss,” Tallulah revealed to Vogue.
Willis shares daughters Tallulah, Rumer, 34, and Scout, 31, with his ex-wife, actor Demi Moore.
He then went on to marry model Emma Heming in 2009 and the couple later welcomed two daughters: Mabel, 11, and Evelyn, 9.
The idea “tortured” Tallulah, which caused her to ignore the symptoms of her father’s rapid health decline. She admitted she was “not proud of” her denial of these warning signs.
“The truth is that I was too sick myself to handle it,” she added, sharing with Vogue that she suffered from anorexia nervosa over the last four years.
She went on to reveal that she had been unwilling to talk about her eating disorder because food restriction felt like “the last vice” that she could keep, after her decision to get sober at 20 years old.
What’s more, when Tallulah was 25, she was admitted to a treatment facility for depression and was later told she had ADHD.
“While I was wrapped up in my body dysmorphia, flaunting it on Instagram, my dad was quietly struggling,” she said.
“All kinds of cognitive testing was being conducted, but we didn’t have an acronym yet. I had managed to give my central dad-feeling canal an epidural; the good feelings weren’t really there, the bad feelings weren’t really there.”
She also recalled realising the “devastating” truth that her dad would never be able to give a speech about her “at my wedding”.
But as Tallulah’s health battles eased, she was able to be fully present in her relationship with her father.
“In the past, I was so afraid of being destroyed by sadness, but finally I feel that I can show up and be relied upon.
“I can savour that time, hold my dad’s hand, and feel that it’s wonderful.
“I know that trials are looming, that this is the beginning of grief, but that whole thing about loving yourself before you can love somebody else – it’s real.”
Lately, Tallulah is grateful for every second she can spend with Willis and takes “tons of photos” whenever she’s with her father.
She revealed that he still recognises her and “lights up” when he sees her but acknowledged “this thing happening with my dad that can shift so quickly and unpredictably”.
Willis, who announced his retirement from acting in March last year, was originally diagnosed with aphasia, a disorder that alters a particular area of the brain that controls language expression and comprehension.
His family said that, while finding out he had FTD was “painful”, they felt a sense of “relief to finally have a clear diagnosis”. The family shared the news in a personal statement on the Association for Frontotemporal Degeneration website.
“FTD is a cruel disease that many of us have never heard of and can strike anyone. For people under 60, FTD is the most common form of dementia and, because getting the diagnosis can take years, FTD is likely much more prevalent than we know,” they continued.
FTD has no treatments or cures. However, patients can be helped by psychologists to cope with their altercations in behaviour and mood.